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/* Copyright (c) 2000, 2023, Oracle and/or its affiliates.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License, version 2.0,
as published by the Free Software Foundation.
This program is also distributed with certain software (including
but not limited to OpenSSL) that is licensed under separate terms,
as designated in a particular file or component or in included license
documentation. The authors of MySQL hereby grant you an additional
permission to link the program and your derivative works with the
separately licensed software that they have included with MySQL.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License, version 2.0, for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
/**
@file
@brief Optimize query expressions: Make optimal table join order, select
optimal access methods per table, apply grouping, sorting and
limit processing.
@defgroup Query_Optimizer Query Optimizer
@{
*/
#include "sql_optimizer.h"
#include "my_bit.h" // my_count_bits
#include "abstract_query_plan.h" // Join_plan
#include "debug_sync.h" // DEBUG_SYNC
#include "item_sum.h" // Item_sum
#include "lock.h" // mysql_unlock_some_tables
#include "opt_explain.h" // join_type_str
#include "opt_trace.h" // Opt_trace_object
#include "sql_base.h" // init_ftfuncs
#include "sql_join_buffer.h" // JOIN_CACHE
#include "sql_parse.h" // check_stack_overrun
#include "sql_planner.h" // calculate_condition_filter
#include "sql_resolver.h" // subquery_allows_materialization
#include "sql_test.h" // print_where
#include "sql_tmp_table.h" // get_max_key_and_part_length
#include "opt_hints.h" // hint_table_state
#include <algorithm>
using std::max;
using std::min;
static bool optimize_semijoin_nests_for_materialization(JOIN *join);
static void calculate_materialization_costs(JOIN *join, TABLE_LIST *sj_nest,
uint n_tables,
Semijoin_mat_optimize *sjm);
static bool make_join_select(JOIN *join, Item *item);
static bool list_contains_unique_index(JOIN_TAB *tab,
bool (*find_func) (Field *, void *), void *data);
static bool find_field_in_item_list (Field *field, void *data);
static bool find_field_in_order_list (Field *field, void *data);
static ORDER *create_distinct_group(THD *thd, Ref_ptr_array ref_pointer_array,
ORDER *order, List<Item> &fields,
List<Item> &all_fields,
bool *all_order_by_fields_used);
static TABLE *get_sort_by_table(ORDER *a,ORDER *b,TABLE_LIST *tables);
static bool add_ref_to_table_cond(THD *thd, JOIN_TAB *join_tab);
static Item *remove_additional_cond(Item* conds);
static void trace_table_dependencies(Opt_trace_context * trace,
JOIN_TAB *join_tabs,
uint table_count);
static bool
update_ref_and_keys(THD *thd, Key_use_array *keyuse,JOIN_TAB *join_tab,
uint tables, Item *cond, COND_EQUAL *cond_equal,
table_map normal_tables, SELECT_LEX *select_lex,
SARGABLE_PARAM **sargables);
static bool pull_out_semijoin_tables(JOIN *join);
static void add_group_and_distinct_keys(JOIN *join, JOIN_TAB *join_tab);
static ha_rows get_quick_record_count(THD *thd, JOIN_TAB *tab, ha_rows limit);
static Item *
make_cond_for_table_from_pred(Item *root_cond, Item *cond,
table_map tables, table_map used_table,
bool exclude_expensive_cond);
static bool
only_eq_ref_tables(JOIN *join, ORDER *order, table_map tables,
table_map *cached_eq_ref_tables, table_map
*eq_ref_tables);
static bool setup_join_buffering(JOIN_TAB *tab, JOIN *join, uint no_jbuf_after);
static bool
test_if_skip_sort_order(JOIN_TAB *tab, ORDER *order, ha_rows select_limit,
const bool no_changes, const key_map *map,
const char *clause_type);
static Item_func_match *test_if_ft_index_order(ORDER *order);
static uint32 get_key_length_tmp_table(Item *item);
/**
Optimizes one query block into a query execution plan (QEP.)
This is the entry point to the query optimization phase. This phase
applies both logical (equivalent) query rewrites, cost-based join
optimization, and rule-based access path selection. Once an optimal
plan is found, the member function creates/initializes all
structures needed for query execution. The main optimization phases
are outlined below:
-# Logical transformations:
- Outer to inner joins transformation.
- Equality/constant propagation.
- Partition pruning.
- COUNT(*), MIN(), MAX() constant substitution in case of
implicit grouping.
- ORDER BY optimization.
-# Perform cost-based optimization of table order and access path
selection. See JOIN::make_join_plan()
-# Post-join order optimization:
- Create optimal table conditions from the where clause and the
join conditions.
- Inject outer-join guarding conditions.
- Adjust data access methods after determining table condition
(several times.)
- Optimize ORDER BY/DISTINCT.
-# Code generation
- Set data access functions.
- Try to optimize away sorting/distinct.
- Setup temporary table usage for grouping and/or sorting.
@retval 0 Success.
@retval 1 Error, error code saved in member JOIN::error.
*/
int
JOIN::optimize()
{
uint no_jbuf_after= UINT_MAX;
DBUG_ENTER("JOIN::optimize");
assert(select_lex->leaf_table_count == 0 ||
thd->lex->is_query_tables_locked() ||
select_lex == unit->fake_select_lex);
assert(tables == 0 &&
primary_tables == 0 &&
tables_list == (TABLE_LIST*)1);
// to prevent double initialization on EXPLAIN
if (optimized)
DBUG_RETURN(0);
Prepare_error_tracker tracker(thd);
DEBUG_SYNC(thd, "before_join_optimize");
THD_STAGE_INFO(thd, stage_optimizing);
if (select_lex->first_execution)
{
/**
@todo
This query block didn't transform itself in SELECT_LEX::prepare(), so
belongs to a parent query block. That parent, or its parents, had to
transform us - it has not; maybe it is itself in prepare() and
evaluating the present query block as an Item_subselect. Such evaluation
in prepare() is expected to be a rare case to be eliminated in the
future ("SET x=(subq)" is one such case; because it locks tables before
prepare()).
*/
if (select_lex->apply_local_transforms(thd, false))
DBUG_RETURN(error= 1);
}
Opt_trace_context * const trace= &thd->opt_trace;
Opt_trace_object trace_wrapper(trace);
Opt_trace_object trace_optimize(trace, "join_optimization");
trace_optimize.add_select_number(select_lex->select_number);
Opt_trace_array trace_steps(trace, "steps");
count_field_types(select_lex, &tmp_table_param, all_fields, false, false);
assert(tmp_table_param.sum_func_count == 0 ||
group_list || implicit_grouping);
if (select_lex->olap == ROLLUP_TYPE && optimize_rollup())
DBUG_RETURN(true); /* purecov: inspected */
if (alloc_func_list())
DBUG_RETURN(1); /* purecov: inspected */
if (select_lex->get_optimizable_conditions(thd, &where_cond, &having_cond))
DBUG_RETURN(1);
set_optimized();
tables_list= select_lex->get_table_list();
/* dump_TABLE_LIST_graph(select_lex, select_lex->leaf_tables); */
/*
Run optimize phase for all derived tables/views used in this SELECT,
including those in semi-joins.
*/
if (select_lex->materialized_derived_table_count)
{
for (TABLE_LIST *tl= select_lex->leaf_tables; tl; tl= tl->next_leaf)
{
if (tl->is_view_or_derived() && tl->optimize_derived(thd))
DBUG_RETURN(1);
}
}
/* dump_TABLE_LIST_graph(select_lex, select_lex->leaf_tables); */
row_limit= ((select_distinct || order || group_list) ?
HA_POS_ERROR : unit->select_limit_cnt);
// m_select_limit is used to decide if we are likely to scan the whole table.
m_select_limit= unit->select_limit_cnt;
if (unit->first_select()->active_options() & OPTION_FOUND_ROWS)
{
/*
Calculate found rows if
- LIMIT is set, and
- Query block is not equipped with "braces". In this case, each
query block must be calculated fully and the limit is applied on
the final UNION evaluation.
*/
calc_found_rows= m_select_limit != HA_POS_ERROR && !select_lex->braces;
}
if (having_cond || calc_found_rows)
m_select_limit= HA_POS_ERROR;
if (unit->select_limit_cnt == 0 && !calc_found_rows)
{
zero_result_cause= "Zero limit";
best_rowcount= 0;
goto setup_subq_exit;
}
if (where_cond || select_lex->outer_join)
{
if (optimize_cond(thd, &where_cond, &cond_equal,
&select_lex->top_join_list, &select_lex->cond_value))
{
error= 1;
DBUG_PRINT("error",("Error from optimize_cond"));
DBUG_RETURN(1);
}
if (select_lex->cond_value == Item::COND_FALSE)
{
zero_result_cause= "Impossible WHERE";
best_rowcount= 0;
goto setup_subq_exit;
}
}
if (having_cond)
{
if (optimize_cond(thd, &having_cond, &cond_equal, NULL,
&select_lex->having_value))
{
error= 1;
DBUG_PRINT("error",("Error from optimize_cond"));
DBUG_RETURN(1);
}
if (select_lex->having_value == Item::COND_FALSE)
{
zero_result_cause= "Impossible HAVING";
best_rowcount= 0;
goto setup_subq_exit;
}
}
if (select_lex->partitioned_table_count && prune_table_partitions())
{
error= 1;
DBUG_PRINT("error", ("Error from prune_partitions"));
DBUG_RETURN(1);
}
/*
Try to optimize count(*), min() and max() to const fields if
there is implicit grouping (aggregate functions but no
group_list). In this case, the result set shall only contain one
row.
*/
if (tables_list && implicit_grouping)
{
int res;
/*
opt_sum_query() returns HA_ERR_KEY_NOT_FOUND if no rows match
the WHERE condition,
or 1 if all items were resolved (optimized away),
or 0, or an error number HA_ERR_...
If all items were resolved by opt_sum_query, there is no need to
open any tables.
*/
if ((res= opt_sum_query(thd, select_lex->leaf_tables, all_fields,
where_cond)))
{
best_rowcount= 0;
if (res == HA_ERR_KEY_NOT_FOUND)
{
DBUG_PRINT("info",("No matching min/max row"));
zero_result_cause= "No matching min/max row";
goto setup_subq_exit;
}
if (res > 1)
{
error= res;
DBUG_PRINT("error",("Error from opt_sum_query"));
DBUG_RETURN(1);
}
if (res < 0)
{
DBUG_PRINT("info",("No matching min/max row"));
zero_result_cause= "No matching min/max row";
goto setup_subq_exit;
}
DBUG_PRINT("info",("Select tables optimized away"));
zero_result_cause= "Select tables optimized away";
tables_list= 0; // All tables resolved
best_rowcount= 1;
const_tables= tables= primary_tables= select_lex->leaf_table_count;
/*
Extract all table-independent conditions and replace the WHERE
clause with them. All other conditions were computed by opt_sum_query
and the MIN/MAX/COUNT function(s) have been replaced by constants,
so there is no need to compute the whole WHERE clause again.
Notice that make_cond_for_table() will always succeed to remove all
computed conditions, because opt_sum_query() is applicable only to
conjunctions.
Preserve conditions for EXPLAIN.
*/
if (where_cond && !thd->lex->describe)
{
Item *table_independent_conds=
make_cond_for_table(where_cond, PSEUDO_TABLE_BITS, 0, 0);
DBUG_EXECUTE("where",
print_where(table_independent_conds,
"where after opt_sum_query()",
QT_ORDINARY););
where_cond= table_independent_conds;
}
goto setup_subq_exit;
}
}
if (!tables_list)
{
DBUG_PRINT("info",("No tables"));
best_rowcount= 1;
error= 0;
if (make_tmp_tables_info())
DBUG_RETURN(1);
count_field_types(select_lex, &tmp_table_param, all_fields, false, false);
// Make plan visible for EXPLAIN
set_plan_state(NO_TABLES);
DBUG_RETURN(0);
}
error= -1; // Error is sent to client
sort_by_table= get_sort_by_table(order, group_list, select_lex->leaf_tables);
if ((where_cond || group_list || order) &&
substitute_gc(thd, select_lex, where_cond, group_list, order))
{
// We added hidden fields to the all_fields list, count them.
count_field_types(select_lex, &tmp_table_param, select_lex->all_fields,
false, false);
}
// Set up join order and initial access paths
THD_STAGE_INFO(thd, stage_statistics);
if (make_join_plan())
{
if (thd->killed)
thd->send_kill_message();
DBUG_PRINT("error",("Error: JOIN::make_join_plan() failed"));
DBUG_RETURN(1);
}
// At this stage, join_tab==NULL, JOIN_TABs are listed in order by best_ref.
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
if (zero_result_cause)
goto setup_subq_exit;
if (rollup.state != ROLLUP::STATE_NONE)
{
if (rollup_process_const_fields())
{
DBUG_PRINT("error", ("Error: rollup_process_fields() failed"));
DBUG_RETURN(1);
}
/*
Fields may have been replaced by Item_func_rollup_const, so
recalculate the number of fields and functions for this query block.
*/
// JOIN::optimize_rollup() may set quick_group=0, and we must not undo that.
const uint save_quick_group= tmp_table_param.quick_group;
count_field_types(select_lex, &tmp_table_param, all_fields, false, false);
tmp_table_param.quick_group= save_quick_group;
}
else
{
/* Remove distinct if only const tables */
select_distinct&= !plan_is_const();
}
if (const_tables && !thd->locked_tables_mode &&
!(select_lex->active_options() & SELECT_NO_UNLOCK))
{
TABLE *ct[MAX_TABLES];
for (uint i= 0; i < const_tables; i++)
ct[i]= best_ref[i]->table();
mysql_unlock_some_tables(thd, ct, const_tables);
}
if (!where_cond && select_lex->outer_join)
{
/* Handle the case where we have an OUTER JOIN without a WHERE */
where_cond=new Item_int((longlong) 1,1); // Always true
}
error= 0;
/*
Among the equal fields belonging to the same multiple equality
choose the one that is to be retrieved first and substitute
all references to these in where condition for a reference for
the selected field.
*/
if (where_cond)
{
where_cond= substitute_for_best_equal_field(where_cond, cond_equal,
map2table);
if (thd->is_error())
{
error= 1;
DBUG_PRINT("error",("Error from substitute_for_best_equal"));
DBUG_RETURN(1);
}
where_cond->update_used_tables();
DBUG_EXECUTE("where",
print_where(where_cond,
"after substitute_best_equal",
QT_ORDINARY););
}
/*
Perform the same optimization on field evaluation for all join conditions.
*/
for (uint i= const_tables; i < tables ; ++i)
{
JOIN_TAB *const tab= best_ref[i];
if (tab->position() && tab->join_cond())
{
tab->set_join_cond(substitute_for_best_equal_field(tab->join_cond(),
tab->cond_equal,
map2table));
if (thd->is_error())
{
error= 1;
DBUG_PRINT("error",("Error from substitute_for_best_equal"));
DBUG_RETURN(1);
}
tab->join_cond()->update_used_tables();
}
}
if (init_ref_access())
{
error= 1;
DBUG_PRINT("error",("Error from init_ref_access"));
DBUG_RETURN(1);
}
// Update table dependencies after assigning ref access fields
update_depend_map();
THD_STAGE_INFO(thd, stage_preparing);
if (make_join_select(this, where_cond))
{
if (thd->is_error())
DBUG_RETURN(1);
zero_result_cause=
"Impossible WHERE noticed after reading const tables";
goto setup_subq_exit;
}
if (select_lex->query_result()->initialize_tables(this))
{
DBUG_PRINT("error",("Error: initialize_tables() failed"));
DBUG_RETURN(1); // error == -1
}
error= -1; /* if goto err */
if (optimize_distinct_group_order())
DBUG_RETURN(true);
if ((select_lex->active_options() & SELECT_NO_JOIN_CACHE) ||
select_lex->ftfunc_list->elements)
no_jbuf_after= 0;
/* Perform FULLTEXT search before all regular searches */
if (select_lex->has_ft_funcs() && optimize_fts_query())
DBUG_RETURN(1);
/*
By setting child_subquery_can_materialize so late we gain the following:
JOIN::compare_costs_of_subquery_strategies() can test this variable to
know if we are have finished evaluating constant conditions, which itself
helps determining fanouts.
*/
child_subquery_can_materialize= true;
/*
It's necessary to check const part of HAVING cond as
there is a chance that some cond parts may become
const items after make_join_statisctics(for example
when Item is a reference to const table field from
outer join).
This check is performed only for those conditions
which do not use aggregate functions. In such case
temporary table may not be used and const condition
elements may be lost during further having
condition transformation in JOIN::exec.
*/
if (having_cond && const_table_map && !having_cond->with_sum_func)
{
having_cond->update_used_tables();
if (remove_eq_conds(thd, having_cond, &having_cond,
&select_lex->having_value))
{
error= 1;
DBUG_PRINT("error",("Error from remove_eq_conds"));
DBUG_RETURN(1);
}
if (select_lex->having_value == Item::COND_FALSE)
{
having_cond= new Item_int((longlong) 0,1);
zero_result_cause= "Impossible HAVING noticed after reading const tables";
goto setup_subq_exit;
}
}
/* Cache constant expressions in WHERE, HAVING, ON clauses. */
if (!plan_is_const() && cache_const_exprs())
DBUG_RETURN(1);
// See if this subquery can be evaluated with subselect_indexsubquery_engine
if (const int ret= replace_index_subquery())
{
set_plan_state(PLAN_READY);
/*
We leave optimize() because the rest of it is only about order/group
which those subqueries don't have and about setting up plan which
we're not going to use due to different execution method.
*/
DBUG_RETURN(ret < 0);
}
{
/*
If the hint FORCE INDEX FOR ORDER BY/GROUP BY is used for the first
table (it does not make sense for other tables) then we cannot do join
buffering.
*/
if (!plan_is_const())
{
const TABLE * const first= best_ref[const_tables]->table();
if ((first->force_index_order && order) ||
(first->force_index_group && group_list))
no_jbuf_after= 0;
}
bool simple_sort= true;
// Check whether join cache could be used
for (uint i= const_tables; i < tables; i++)
{
JOIN_TAB *const tab= best_ref[i];
if (!tab->position())
continue;
if (setup_join_buffering(tab, this, no_jbuf_after))
DBUG_RETURN(true);
if (tab->use_join_cache() != JOIN_CACHE::ALG_NONE)
simple_sort= false;
assert(tab->type() != JT_FT ||
tab->use_join_cache() == JOIN_CACHE::ALG_NONE);
}
if (!simple_sort)
{
/*
A join buffer is used for this table. We here inform the optimizer
that it should not rely on rows of the first non-const table being in
order thanks to an index scan; indeed join buffering of the present
table subsequently changes the order of rows.
*/
simple_order= simple_group= false;
}
}
if (!plan_is_const() && order)
{
/*
Force using of tmp table if sorting by a SP or UDF function due to
their expensive and probably non-deterministic nature.
*/
for (ORDER *tmp_order= order; tmp_order ; tmp_order=tmp_order->next)
{
Item *item= *tmp_order->item;
if (item->is_expensive())
{
/* Force tmp table without sort */
simple_order= simple_group= false;
break;
}
}
}
/*
Check if we need to create a temporary table.
This has to be done if all tables are not already read (const tables)
and one of the following conditions holds:
- We are using DISTINCT (simple distinct's have already been optimized away)
- We are using an ORDER BY or GROUP BY on fields not in the first table
- We are using different ORDER BY and GROUP BY orders
- The user wants us to buffer the result.
When the WITH ROLLUP modifier is present, we cannot skip temporary table
creation for the DISTINCT clause just because there are only const tables.
*/
need_tmp= ((!plan_is_const() &&
((select_distinct || (order && !simple_order) ||
(group_list && !simple_group)) ||
(group_list && order) ||
(select_lex->active_options() & OPTION_BUFFER_RESULT))) ||
(rollup.state != ROLLUP::STATE_NONE && select_distinct));
DBUG_EXECUTE("info", TEST_join(this););
if (!plan_is_const())
{
JOIN_TAB *tab= best_ref[const_tables];
/*
Because filesort always does a full table scan or a quick range scan
we must add the removed reference to the select for the table.
We only need to do this when we have a simple_order or simple_group
as in other cases the join is done before the sort.
*/
if ((order || group_list) &&
tab->type() != JT_ALL &&
tab->type() != JT_FT &&
tab->type() != JT_REF_OR_NULL &&
((order && simple_order) || (group_list && simple_group)))
{
if (add_ref_to_table_cond(thd,tab)) {
DBUG_RETURN(1);
}
}
// Test if we can use an index instead of sorting
test_skip_sort();
}
if (alloc_qep(tables))
DBUG_RETURN(error= 1); /* purecov: inspected */
if (make_join_readinfo(this, no_jbuf_after))
DBUG_RETURN(1); /* purecov: inspected */
if (make_tmp_tables_info())
DBUG_RETURN(1);
// At this stage, we have fully set QEP_TABs; JOIN_TABs are unaccessible,
// pushed joins(see below) are still allowed to change the QEP_TABs
/*
Push joins to handlerton(s)
The handlerton(s) will inspect the QEP through the
AQP (Abstract Query Plan) and extract from it whatever
it might implement of pushed execution.
It is the responsibility of the handler:
- to store any information it need for later
execution of pushed queries.
- to call appropriate AQP functions which modifies the
QEP to use the special 'linked' read functions
for those parts of the join which have been pushed.
Currently pushed joins are only implemented by NDB.
It only make sense to try pushing if > 1 non-const tables.
*/
if (!plan_is_single_table() && !plan_is_const())
{
const AQP::Join_plan plan(this);
if (ha_make_pushed_joins(thd, &plan))
DBUG_RETURN(1);
}
// Update m_current_query_cost to reflect actual need of filesort.
if (sort_cost > 0.0 && !explain_flags.any(ESP_USING_FILESORT))
{
best_read-= sort_cost;
sort_cost= 0.0;
if (thd->lex->is_single_level_stmt())
thd->m_current_query_cost= best_read;
}
count_field_types(select_lex, &tmp_table_param, all_fields, false, false);
// Make plan visible for EXPLAIN
set_plan_state(PLAN_READY);
DEBUG_SYNC(thd, "after_join_optimize");
error= 0;
DBUG_RETURN(0);
setup_subq_exit:
assert(zero_result_cause != NULL);
/*
Even with zero matching rows, subqueries in the HAVING clause may
need to be evaluated if there are aggregate functions in the
query. If this JOIN is part of an outer query, subqueries in HAVING may
be evaluated several times in total; so subquery materialization makes
sense.
*/
child_subquery_can_materialize= true;
trace_steps.end(); // because all steps are done
Opt_trace_object(trace, "empty_result")
.add_alnum("cause", zero_result_cause);
having_for_explain= having_cond;
error= 0;
if (!qep_tab && best_ref)
{
/*
After creation of JOIN_TABs in make_join_plan(), we have shortcut due to
some zero_result_cause. For simplification, if we have JOIN_TABs we
want QEP_TABs too.
*/
if (alloc_qep(tables))
DBUG_RETURN(1); /* purecov: inspected */
unplug_join_tabs();
}
set_plan_state(ZERO_RESULT);
DBUG_RETURN(0);
}
/**
Substitute all expressions in the WHERE condition and ORDER/GROUP lists
that match generated columns (GC) expressions with GC fields, if any.
@details This function does 3 things:
1) Creates list of all GC fields that are a part of a key and the GC
expression is a function. All query tables are scanned. If there's no
such fields, function exits.
2) By means of Item::compile() WHERE clause is transformed.
@see Item_func::gc_subst_transformer() for details.
3) If there's ORDER/GROUP BY clauses, this function tries to substitute
expressions in these lists with GC too. It removes from the list of
indexed GC all elements which index blocked by hints. This is done to
reduce amount of further work. Next it goes through ORDER/GROUP BY list
and matches the expression in it against GC expressions in indexed GC
list. When a match is found, the expression is replaced with a new
Item_field for the matched GC field. Also, this new field is added to
the hidden part of all_fields list.
@param thd thread handle
@param select_lex the current select
@param where_cond the WHERE condition, possibly NULL
@param group_list the GROUP BY clause, possibly NULL
@param order the ORDER BY clause, possibly NULL
@return true if the GROUP BY clause or the ORDER BY clause was
changed, false otherwise
*/
bool substitute_gc(THD *thd, SELECT_LEX *select_lex, Item *where_cond,
ORDER *group_list, ORDER *order)
{
List<Field> indexed_gc;
Opt_trace_context * const trace= &thd->opt_trace;
Opt_trace_object trace_wrapper(trace);
Opt_trace_object subst_gc(trace, "substitute_generated_columns");
// Collect all GCs that are a part of a key
for (TABLE_LIST *tl= select_lex->leaf_tables;
tl;
tl= tl->next_leaf)
{
if (tl->table->s->keys == 0)
continue;
for (uint i= 0; i < tl->table->s->fields; i++)
{
Field *fld= tl->table->field[i];
if (fld->is_gcol() && !fld->part_of_key.is_clear_all() &&
fld->gcol_info->expr_item->can_be_substituted_for_gc())
{
// Don't check allowed keys here as conditions/group/order use
// different keymaps for that.
indexed_gc.push_back(fld);
}
}
}
// No GC in the tables used in the query
if (indexed_gc.elements == 0)
return false;
if (where_cond)
{
// Item_func::compile will dereference this pointer, provide valid value.
uchar i, *dummy= &i;
where_cond->compile(&Item::gc_subst_analyzer, &dummy,
&Item::gc_subst_transformer, (uchar*) &indexed_gc);
subst_gc.add("resulting_condition", where_cond);
}
if (!(group_list || order))
return false;
// Filter out GCs that do not have index usable for GROUP/ORDER
Field *gc;
List_iterator<Field> li(indexed_gc);
while ((gc= li++))
{
key_map tkm= gc->part_of_key;
tkm.intersect(group_list ? gc->table->keys_in_use_for_group_by :
gc->table->keys_in_use_for_order_by);
if (tkm.is_clear_all())
li.remove();
}
if (!indexed_gc.elements)
return false;
// Index could be used for ORDER only if there is no GROUP
ORDER *list= group_list ? group_list : order;
bool changed= false;
for (ORDER *ord= list; ord; ord= ord->next)
{
li.rewind();
if (!(*ord->item)->can_be_substituted_for_gc())
continue;
while ((gc= li++))
{
Item_func *tmp= pointer_cast<Item_func*>(*ord->item);
Item_field *field;
if ((field= get_gc_for_expr(&tmp, gc, gc->result_type())))
{
changed= true;
/* Add new field to field list. */
ord->item= select_lex->add_hidden_item(field);
break;
}
}
}
if (changed && trace->is_started())
{
String str;
st_select_lex::print_order(&str, list,
enum_query_type(QT_TO_SYSTEM_CHARSET |
QT_SHOW_SELECT_NUMBER |
QT_NO_DEFAULT_DB));
subst_gc.add_utf8(group_list ? "resulting_GROUP_BY" :
"resulting_ORDER_BY",
str.ptr(), str.length());
}
return changed;
}
/**
Sets the plan's state of the JOIN. This is always the final step of
optimization; starting from this call, we expose the plan to other
connections (via EXPLAIN CONNECTION) so the plan has to be final.
QEP_TAB's quick_optim, condition_optim and keyread_optim are set here.
*/
void JOIN::set_plan_state(enum_plan_state plan_state_arg)
{
// A plan should not change to another plan:
assert(plan_state_arg == NO_PLAN || plan_state == NO_PLAN);
if (plan_state == NO_PLAN && plan_state_arg != NO_PLAN)
{
if (qep_tab != NULL)
{
/*
We want to cover primary tables, tmp tables (they may have a sort, so
their "quick" and "condition" may change when execution runs the
sort), and sj-mat inner tables. Note that make_tmp_tables_info() may
have added a sort to the first non-const primary table, so it's
important to do those assignments after make_tmp_tables_info().
*/
for (uint i= const_tables; i < tables; ++i)
{
qep_tab[i].set_quick_optim();
qep_tab[i].set_condition_optim();
qep_tab[i].set_keyread_optim();
}
}
}
DEBUG_SYNC(thd, "before_set_plan");
// If SQLCOM_END, no thread is explaining our statement anymore.
const bool need_lock= thd->query_plan.get_command() != SQLCOM_END;
if (need_lock)
thd->lock_query_plan();
plan_state= plan_state_arg;
if (need_lock)
thd->unlock_query_plan();
}
bool JOIN::alloc_qep(uint n)
{
// Just to be sure that type plan_idx is wide enough:
compile_time_assert(MAX_TABLES <= INT_MAX8);
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
qep_tab= new(thd->mem_root) QEP_TAB[n];
if (!qep_tab)
return true; /* purecov: inspected */
for (uint i= 0; i < n; ++i)
qep_tab[i].init(best_ref[i]);
return false;
}
void QEP_TAB::init(JOIN_TAB *jt)
{
jt->share_qs(this);
set_table(table()); // to update table()->reginfo.qep_tab
table_ref= jt->table_ref;
}
/// @returns semijoin strategy for this table.
uint QEP_TAB::get_sj_strategy() const
{
if (first_sj_inner() == NO_PLAN_IDX)
return SJ_OPT_NONE;
const uint s= join()->qep_tab[first_sj_inner()].position()->sj_strategy;
assert(s != SJ_OPT_NONE);
return s;
}
/**
Return the index used for a table in a QEP
The various access methods have different places where the index/key
number is stored, so this function is needed to return the correct value.
@returns index number, or MAX_KEY if not applicable.
JT_SYSTEM and JT_ALL does not use an index, and will always return MAX_KEY.
JT_INDEX_MERGE supports more than one index. Hence MAX_KEY is returned and
a further inspection is needed.
*/
uint QEP_TAB::effective_index() const
{
switch (type())
{
case JT_SYSTEM:
assert(ref().key == -1);
return MAX_KEY;
case JT_CONST:
case JT_EQ_REF:
case JT_REF_OR_NULL:
case JT_REF:
assert(ref().key != -1);
return uint(ref().key);
case JT_INDEX_SCAN:
case JT_FT:
return index();
case JT_INDEX_MERGE:
assert(quick()->index == MAX_KEY);
return MAX_KEY;
case JT_RANGE:
return quick()->index;
case JT_ALL:
default:
// @todo Check why JT_UNKNOWN is a valid value here.
assert(type() == JT_ALL || type() == JT_UNKNOWN);
return MAX_KEY;
}
}
uint JOIN_TAB::get_sj_strategy() const
{
if (first_sj_inner() == NO_PLAN_IDX)
return SJ_OPT_NONE;
ASSERT_BEST_REF_IN_JOIN_ORDER(join());
JOIN_TAB *tab= join()->best_ref[first_sj_inner()];
uint s= tab->position()->sj_strategy;
assert(s != SJ_OPT_NONE);
return s;
}
int JOIN::replace_index_subquery()
{
DBUG_ENTER("replace_index_subquery");
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
if (group_list ||
!(unit->item && unit->item->substype() == Item_subselect::IN_SUBS) ||
primary_tables != 1 || !where_cond ||
unit->is_union())
DBUG_RETURN(0);
// Guaranteed by remove_redundant_subquery_clauses():
assert(order == NULL && !select_distinct);
subselect_engine *engine= NULL;
Item_in_subselect * const in_subs=
static_cast<Item_in_subselect *>(unit->item);
enum join_type type= JT_UNKNOWN;
JOIN_TAB *const first_join_tab= best_ref[0];
if (in_subs->exec_method == Item_exists_subselect::EXEC_MATERIALIZATION)
{
// We cannot have two engines at the same time
}
else if (having_cond == NULL)
{
if (first_join_tab->type() == JT_EQ_REF &&
first_join_tab->ref().items[0]->item_name.ptr() == in_left_expr_name)
{
type= JT_UNIQUE_SUBQUERY;
/*
This uses test_if_ref(), which needs access to JOIN_TAB::join_cond() so
it must be done before we get rid of JOIN_TAB.
*/
remove_subq_pushed_predicates();
}
else if (first_join_tab->type() == JT_REF &&
first_join_tab->ref().items[0]->item_name.ptr() == in_left_expr_name)
{
type= JT_INDEX_SUBQUERY;
remove_subq_pushed_predicates();
}
}
else if (first_join_tab->type() == JT_REF_OR_NULL &&
first_join_tab->ref().items[0]->item_name.ptr() == in_left_expr_name &&
having_cond->item_name.ptr() == in_having_cond)
{
type= JT_INDEX_SUBQUERY;
where_cond= remove_additional_cond(where_cond);
}
if (type == JT_UNKNOWN)
DBUG_RETURN(0);
if (alloc_qep(tables))
DBUG_RETURN(-1); /* purecov: inspected */
unplug_join_tabs();
error= 0;
QEP_TAB *const first_qep_tab= &qep_tab[0];
if (first_qep_tab->table()->covering_keys.is_set(first_qep_tab->ref().key))
{
assert(!first_qep_tab->table()->no_keyread);
first_qep_tab->table()->set_keyread(true);
}
// execution uses where_cond:
first_qep_tab->set_condition(where_cond);
engine=
new subselect_indexsubquery_engine(thd, first_qep_tab, unit->item,
where_cond,
having_cond,
// check_null
first_qep_tab->type() == JT_REF_OR_NULL,
// unique
type == JT_UNIQUE_SUBQUERY);
/**
@todo If having_cond!=NULL we pass unique=false. But for this query:
(oe1, oe2) IN (SELECT primary_key, non_key_maybe_null_field FROM tbl)
we could use "unique=true" for the first index component and let
Item_is_not_null_test(non_key_maybe_null_field) handle the second.
*/
first_qep_tab->set_type(type);
if (!unit->item->change_engine(engine))
DBUG_RETURN(1);
else // error:
DBUG_RETURN(-1); /* purecov: inspected */
}
bool JOIN::optimize_distinct_group_order()
{
DBUG_ENTER("optimize_distinct_group_order");
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
/* Optimize distinct away if possible */
{
ORDER *org_order= order;
order= ORDER_with_src(remove_const(order, where_cond, 1, &simple_order,
"ORDER BY"),
order.src);
if (thd->is_error())
{
error= 1;
DBUG_PRINT("error",("Error from remove_const"));
DBUG_RETURN(true);
}
/*
If we are using ORDER BY NULL or ORDER BY const_expression,
return result in any order (even if we are using a GROUP BY)
*/
if (!order && org_order)
skip_sort_order= 1;
}
/*
Check if we can optimize away GROUP BY/DISTINCT.
We can do that if there are no aggregate functions, the
fields in DISTINCT clause (if present) and/or columns in GROUP BY
(if present) contain direct references to all key parts of
an unique index (in whatever order) and if the key parts of the
unique index cannot contain NULLs.
Note that the unique keys for DISTINCT and GROUP BY should not
be the same (as long as they are unique).
The FROM clause must contain a single non-constant table.
@todo Apart from the LIS test, every condition depends only on facts
which can be known in SELECT_LEX::prepare(), possibly this block should
move there.
*/
JOIN_TAB *const tab= best_ref[const_tables];
if (plan_is_single_table() &&
(group_list || select_distinct) &&
!tmp_table_param.sum_func_count &&
(!tab->quick() ||
tab->quick()->get_type() !=
QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX))
{
if (group_list && rollup.state == ROLLUP::STATE_NONE &&
list_contains_unique_index(tab,
find_field_in_order_list,
(void *) group_list))
{
/*
We have found that grouping can be removed since groups correspond to
only one row anyway, but we still have to guarantee correct result
order. The line below effectively rewrites the query from GROUP BY
<fields> to ORDER BY <fields>. There are three exceptions:
- if skip_sort_order is set (see above), then we can simply skip
GROUP BY;
- if IN(subquery), likewise (see remove_redundant_subquery_clauses())
- we can only rewrite ORDER BY if the ORDER BY fields are 'compatible'
with the GROUP BY ones, i.e. either one is a prefix of another.
We only check if the ORDER BY is a prefix of GROUP BY. In this case
test_if_subpart() copies the ASC/DESC attributes from the original
ORDER BY fields.
If GROUP BY is a prefix of ORDER BY, then it is safe to leave
'order' as is.
*/
if (!order || test_if_subpart(group_list, order))
order= (skip_sort_order ||
(unit->item && unit->item->substype() ==
Item_subselect::IN_SUBS)) ? NULL : group_list;
/*
If we have an IGNORE INDEX FOR GROUP BY(fields) clause, this must be
rewritten to IGNORE INDEX FOR ORDER BY(fields).
*/
best_ref[0]->table()->keys_in_use_for_order_by=
best_ref[0]->table()->keys_in_use_for_group_by;
group_list= 0;
grouped= false;
}
if (select_distinct &&
list_contains_unique_index(tab,
find_field_in_item_list,
(void *) &fields_list))
{
select_distinct= 0;
}
}
if (!(group_list || tmp_table_param.sum_func_count) &&
select_distinct &&
plan_is_single_table() &&
rollup.state == ROLLUP::STATE_NONE)
{
/*
We are only using one table. In this case we change DISTINCT to a
GROUP BY query if:
- The GROUP BY can be done through indexes (no sort) and the ORDER
BY only uses selected fields.
(In this case we can later optimize away GROUP BY and ORDER BY)
- We are scanning the whole table without LIMIT
This can happen if:
- We are using CALC_FOUND_ROWS
- We are using an ORDER BY that can't be optimized away.
We don't want to use this optimization when we are using LIMIT
because in this case we can just create a temporary table that
holds LIMIT rows and stop when this table is full.
*/
if (order)
{
skip_sort_order=
test_if_skip_sort_order(tab, order, m_select_limit,
true, // no_changes
&tab->table()->keys_in_use_for_order_by,
"ORDER BY");
count_field_types(select_lex, &tmp_table_param, all_fields, false, false);
}
ORDER *o;
bool all_order_fields_used;
if ((o= create_distinct_group(thd, ref_ptrs,
order, fields_list, all_fields,
&all_order_fields_used)))
{
group_list= ORDER_with_src(o, ESC_DISTINCT);
const bool skip_group=
skip_sort_order &&
test_if_skip_sort_order(tab, group_list, m_select_limit,
true, // no_changes
&tab->table()->keys_in_use_for_group_by,
"GROUP BY");
count_field_types(select_lex, &tmp_table_param, all_fields, false, false);
if ((skip_group && all_order_fields_used) ||
m_select_limit == HA_POS_ERROR ||
(order && !skip_sort_order))
{
/* Change DISTINCT to GROUP BY */
select_distinct= 0;
no_order= !order;
if (all_order_fields_used)
{
if (order && skip_sort_order)
{
/*
Force MySQL to read the table in sorted order to get result in
ORDER BY order.
*/
tmp_table_param.quick_group=0;
}
order=0;
}
grouped= true; // For end_write_group
}
else
group_list= 0;
}
else if (thd->is_fatal_error) // End of memory
DBUG_RETURN(true);
}
simple_group= 0;
{
ORDER *old_group_list= group_list;
group_list= ORDER_with_src(remove_const(group_list, where_cond,
rollup.state == ROLLUP::STATE_NONE,
&simple_group, "GROUP BY"),
group_list.src);
if (thd->is_error())
{
error= 1;
DBUG_PRINT("error",("Error from remove_const"));
DBUG_RETURN(true);
}
if (old_group_list && !group_list)
select_distinct= 0;
}
if (!group_list && grouped)
{
order=0; // The output has only one row
simple_order=1;
select_distinct= 0; // No need in distinct for 1 row
group_optimized_away= 1;
}
calc_group_buffer(this, group_list);
send_group_parts= tmp_table_param.group_parts; /* Save org parts */
if (test_if_subpart(group_list, order) ||
(!group_list && tmp_table_param.sum_func_count))
{
order=0;
if (is_indexed_agg_distinct(this, NULL))
sort_and_group= 0;
}
DBUG_RETURN(false);
}
void JOIN::test_skip_sort()
{
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
JOIN_TAB *const tab= best_ref[const_tables];
assert(ordered_index_usage == ordered_index_void);
if (group_list) // GROUP BY honoured first
// (DISTINCT was rewritten to GROUP BY if skippable)
{
/*
When there is SQL_BIG_RESULT do not sort using index for GROUP BY,
and thus force sorting on disk unless a group min-max optimization
is going to be used as it is applied now only for one table queries
with covering indexes.
*/
if (!(select_lex->active_options() & SELECT_BIG_RESULT || with_json_agg) ||
(tab->quick() &&
tab->quick()->get_type() ==
QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX))
{
if (simple_group && // GROUP BY is possibly skippable
!select_distinct) // .. if not preceded by a DISTINCT
{
/*
Calculate a possible 'limit' of table rows for 'GROUP BY':
A specified 'LIMIT' is relative to the final resultset.
'need_tmp' implies that there will be more postprocessing
so the specified 'limit' should not be enforced yet.
*/
const ha_rows limit = need_tmp ? HA_POS_ERROR : m_select_limit;
if (test_if_skip_sort_order(tab, group_list, limit, false,
&tab->table()->keys_in_use_for_group_by,
"GROUP BY"))
{
ordered_index_usage= ordered_index_group_by;
}
}
/*
If we are going to use semi-join LooseScan, it will depend
on the selected index scan to be used. If index is not used
for the GROUP BY, we risk that sorting is put on the LooseScan
table. In order to avoid this, force use of temporary table.
TODO: Explain the quick_group part of the test below.
*/
if ((ordered_index_usage != ordered_index_group_by) &&
(tmp_table_param.quick_group ||
(tab->emb_sj_nest &&
tab->position()->sj_strategy == SJ_OPT_LOOSE_SCAN)))
{
need_tmp= true;
simple_order= simple_group= false; // Force tmp table without sort
}
}
}
else if (order && // ORDER BY wo/ preceding GROUP BY
(simple_order || skip_sort_order)) // which is possibly skippable
{
if (test_if_skip_sort_order(tab, order, m_select_limit, false,
&tab->table()->keys_in_use_for_order_by,
"ORDER BY"))
{
ordered_index_usage= ordered_index_order_by;
}
}
}
/**
Test if ORDER BY is a single MATCH function(ORDER BY MATCH)
and sort order is descending.
@param order pointer to ORDER struct.
@retval
Pointer to MATCH function if order is 'ORDER BY MATCH() DESC'
@retval
NULL otherwise
*/
static Item_func_match *test_if_ft_index_order(ORDER *order)
{
if (order && order->next == NULL &&
order->direction == ORDER::ORDER_DESC &&
(*order->item)->type() == Item::FUNC_ITEM &&
((Item_func*) (*order->item))->functype() == Item_func::FT_FUNC)
return static_cast<Item_func_match*> (*order->item)->get_master();
return NULL;
}
/**
Test if this is a prefix index.
@param table table
@param idx index to check
@return TRUE if this is a prefix index
*/
bool is_prefix_index(TABLE* table, uint idx)
{
if (!table || !table->key_info)
{
return false;
}
KEY* key_info = table->key_info;
uint key_parts = key_info[idx].user_defined_key_parts;
KEY_PART_INFO* key_part = key_info[idx].key_part;
for (uint i = 0; i < key_parts; i++, key_part++)
{
if (key_part->field &&
(key_part->length !=
table->field[key_part->fieldnr - 1]->key_length() &&
!(key_info->flags & (HA_FULLTEXT | HA_SPATIAL))))
{
return true;
}
}
return false;
}
/**
Test if one can use the key to resolve ordering.
@param order Sort order
@param table Table to sort
@param idx Index to check
@param[out] used_key_parts NULL by default, otherwise return value for
used key parts.
@note
used_key_parts is set to correct key parts used if return value != 0
(On other cases, used_key_part may be changed)
Note that the value may actually be greater than the number of index
key parts. This can happen for storage engines that have the primary
key parts as a suffix for every secondary key.
@retval
1 key is ok.
@retval
0 Key can't be used
@retval
-1 Reverse key can be used
*/
int test_if_order_by_key(ORDER *order, TABLE *table, uint idx,
uint *used_key_parts)
{
KEY_PART_INFO *key_part,*key_part_end;
key_part=table->key_info[idx].key_part;
key_part_end=key_part+table->key_info[idx].user_defined_key_parts;
key_part_map const_key_parts=table->const_key_parts[idx];
int reverse=0;
uint key_parts;
my_bool on_pk_suffix= FALSE;
DBUG_ENTER("test_if_order_by_key");
for (; order ; order=order->next, const_key_parts>>=1)
{
/*
Since only fields can be indexed, ORDER BY <something> that is
not a field cannot be resolved by using an index.
*/
Item *real_itm= (*order->item)->real_item();
if (real_itm->type() != Item::FIELD_ITEM)
DBUG_RETURN(0);
Field *field= static_cast<Item_field*>(real_itm)->field;
int flag;
/*
Skip key parts that are constants in the WHERE clause.
These are already skipped in the ORDER BY by const_expression_in_where()
*/
for (; const_key_parts & 1 && key_part < key_part_end ;
const_key_parts>>= 1)
key_part++;
/* Avoid usage of prefix index for sorting a partition table */
if (table->part_info && key_part != table->key_info[idx].key_part &&
key_part != key_part_end && is_prefix_index(table, idx))
DBUG_RETURN(0);
if (key_part == key_part_end)
{
/*
We are at the end of the key. Check if the engine has the primary
key as a suffix to the secondary keys. If it has continue to check
the primary key as a suffix.
*/
if (!on_pk_suffix &&
(table->file->ha_table_flags() & HA_PRIMARY_KEY_IN_READ_INDEX) &&
table->s->primary_key != MAX_KEY &&
table->s->primary_key != idx)
{
on_pk_suffix= TRUE;
key_part= table->key_info[table->s->primary_key].key_part;
key_part_end=key_part +
table->key_info[table->s->primary_key].user_defined_key_parts;
const_key_parts=table->const_key_parts[table->s->primary_key];
for (; const_key_parts & 1 ; const_key_parts>>= 1)
key_part++;
/*
The primary and secondary key parts were all const (i.e. there's
one row). The sorting doesn't matter.
*/
if (key_part == key_part_end && reverse == 0)
{
key_parts= 0;
reverse= 1;
goto ok;
}
}
else
DBUG_RETURN(0);
}
if (key_part->field != field || !field->part_of_sortkey.is_set(idx))
DBUG_RETURN(0);
const ORDER::enum_order keypart_order=
(key_part->key_part_flag & HA_REVERSE_SORT) ?
ORDER::ORDER_DESC : ORDER::ORDER_ASC;
/* set flag to 1 if we can use read-next on key, else to -1 */
flag= (order->direction == keypart_order) ? 1 : -1;
if (reverse && flag != reverse)
DBUG_RETURN(0);
reverse=flag; // Remember if reverse
key_part++;
}
if (on_pk_suffix)
{
uint used_key_parts_secondary= table->key_info[idx].user_defined_key_parts;
uint used_key_parts_pk=
(uint) (key_part - table->key_info[table->s->primary_key].key_part);
key_parts= used_key_parts_pk + used_key_parts_secondary;
if (reverse == -1 &&
(!(table->file->index_flags(idx, used_key_parts_secondary - 1, 1) &
HA_READ_PREV) ||
!(table->file->index_flags(table->s->primary_key,
used_key_parts_pk - 1, 1) & HA_READ_PREV)))
reverse= 0; // Index can't be used
}
else
{
key_parts= (uint) (key_part - table->key_info[idx].key_part);
if (reverse == -1 &&
!(table->file->index_flags(idx, key_parts-1, 1) & HA_READ_PREV))
reverse= 0; // Index can't be used
}
ok:
if (used_key_parts != NULL)
*used_key_parts= key_parts;
DBUG_RETURN(reverse);
}
/**
Find shortest key suitable for full table scan.
@param table Table to scan
@param usable_keys Allowed keys
@note
As far as
1) clustered primary key entry data set is a set of all record
fields (key fields and not key fields) and
2) secondary index entry data is a union of its key fields and
primary key fields (at least InnoDB and its derivatives don't
duplicate primary key fields there, even if the primary and
the secondary keys have a common subset of key fields),
then secondary index entry data is always a subset of primary key entry.
Unfortunately, key_info[nr].key_length doesn't show the length
of key/pointer pair but a sum of key field lengths only, thus
we can't estimate index IO volume comparing only this key_length
value of secondary keys and clustered PK.
So, try secondary keys first, and choose PK only if there are no
usable secondary covering keys or found best secondary key include
all table fields (i.e. same as PK):
@return
MAX_KEY no suitable key found
key index otherwise
*/
uint find_shortest_key(TABLE *table, const key_map *usable_keys)
{
uint best= MAX_KEY;
uint usable_clustered_pk= (table->file->primary_key_is_clustered() &&
table->s->primary_key != MAX_KEY &&
usable_keys->is_set(table->s->primary_key)) ?
table->s->primary_key : MAX_KEY;
if (!usable_keys->is_clear_all())
{
uint min_length= (uint) ~0;
for (uint nr=0; nr < table->s->keys ; nr++)
{
if (nr == usable_clustered_pk)
continue;
if (usable_keys->is_set(nr))
{
/*
Can not do full index scan on rtree index because it is not
supported by Innodb, probably not supported by others either.
*/
const KEY &key_ref= table->key_info[nr];
if (key_ref.key_length < min_length &&
!(key_ref.flags & HA_SPATIAL))
{
min_length=key_ref.key_length;
best=nr;
}
}
}
}
if (usable_clustered_pk != MAX_KEY)
{
/*
If the primary key is clustered and found shorter key covers all table
fields then primary key scan normally would be faster because amount of
data to scan is the same but PK is clustered.
It's safe to compare key parts with table fields since duplicate key
parts aren't allowed.
*/
if (best == MAX_KEY ||
table->key_info[best].user_defined_key_parts >= table->s->fields)
best= usable_clustered_pk;
}
return best;
}
/**
Test if a second key is the subkey of the first one.
@param key_part First key parts
@param ref_key_part Second key parts
@param ref_key_part_end Last+1 part of the second key
@note
Second key MUST be shorter than the first one.
@retval
1 is a subkey
@retval
0 no sub key
*/
inline bool
is_subkey(KEY_PART_INFO *key_part, KEY_PART_INFO *ref_key_part,
KEY_PART_INFO *ref_key_part_end)
{
for (; ref_key_part < ref_key_part_end; key_part++, ref_key_part++)
if (!key_part->field->eq(ref_key_part->field))
return 0;
return 1;
}
/**
Test if REF_OR_NULL optimization will be used if the specified
ref_key is used for REF-access to 'tab'
@retval
true JT_REF_OR_NULL will be used
@retval
false no JT_REF_OR_NULL access
*/
static bool
is_ref_or_null_optimized(const JOIN_TAB *tab, uint ref_key)
{
if (tab->keyuse())
{
const Key_use *keyuse= tab->keyuse();
while (keyuse->key != ref_key && keyuse->table_ref == tab->table_ref)
keyuse++;
const table_map const_tables= tab->join()->const_table_map;
while (keyuse->key == ref_key && keyuse->table_ref == tab->table_ref)
{
if (!(keyuse->used_tables & ~const_tables))
{
if (keyuse->optimize & KEY_OPTIMIZE_REF_OR_NULL)
return true;
}
keyuse++;
}
}
return false;
}
/**
Test if we can use one of the 'usable_keys' instead of 'ref' key
for sorting.
@param ref Number of key, used for WHERE clause
@param usable_keys Keys for testing
@return
- MAX_KEY If we can't use other key
- the number of found key Otherwise
*/
static uint
test_if_subkey(ORDER *order, JOIN_TAB *tab, uint ref, uint ref_key_parts,
const key_map *usable_keys)
{
uint nr;
uint min_length= (uint) ~0;
uint best= MAX_KEY;
TABLE *table= tab->table();
KEY_PART_INFO *ref_key_part= table->key_info[ref].key_part;
KEY_PART_INFO *ref_key_part_end= ref_key_part + ref_key_parts;
for (nr= 0 ; nr < table->s->keys ; nr++)
{
if (usable_keys->is_set(nr) &&
table->key_info[nr].key_length < min_length &&
table->key_info[nr].user_defined_key_parts >= ref_key_parts &&
is_subkey(table->key_info[nr].key_part, ref_key_part,
ref_key_part_end) &&
!is_ref_or_null_optimized(tab, nr) &&
test_if_order_by_key(order, table, nr))
{
min_length= table->key_info[nr].key_length;
best= nr;
}
}
return best;
}
/**
It is not obvious to see that test_if_skip_sort_order() never changes the
plan if no_changes is true. So we double-check: creating an instance of this
class saves some important access-path-related information of the current
table; when the instance is destroyed, the latest access-path information is
compared with saved data.
*/
class Plan_change_watchdog
{
#ifndef NDEBUG
public:
/**
@param tab_arg table whose access path is being determined
@param no_changes whether a change to the access path is allowed
*/
Plan_change_watchdog(const JOIN_TAB *tab_arg, const bool no_changes_arg)
{
// Only to keep gcc 4.1.2-44 silent about uninitialized variables
quick= NULL;
quick_index= 0;
if (no_changes_arg)
{
tab= tab_arg;
type= tab->type();
if ((quick= tab->quick()))
quick_index= quick->index;
use_quick= tab->use_quick;
ref_key= tab->ref().key;
ref_key_parts= tab->ref().key_parts;
index= tab->index();
}
else
{
tab= NULL;
// Only to keep gcc 4.1.2-44 silent about uninitialized variables
type= JT_UNKNOWN;
quick= NULL;
ref_key= ref_key_parts= index= 0;
use_quick= QS_NONE;
}
}
~Plan_change_watchdog()
{
if (tab == NULL)
return;
// changes are not allowed, we verify:
assert(tab->type() == type);
assert(tab->quick() == quick);
assert((quick == NULL) || tab->quick()->index == quick_index);
assert(tab->use_quick == use_quick);
assert(tab->ref().key == ref_key);
assert(tab->ref().key_parts == ref_key_parts);
assert(tab->index() == index);
}
private:
const JOIN_TAB *tab; ///< table, or NULL if changes are allowed
enum join_type type; ///< copy of tab->type()
// "Range / index merge" info
const QUICK_SELECT_I *quick; ///< copy of tab->select->quick
uint quick_index; ///< copy of tab->select->quick->index
enum quick_type use_quick; ///< copy of tab->use_quick
// "ref access" info
int ref_key; ///< copy of tab->ref().key
uint ref_key_parts;/// copy of tab->ref().key_parts
// Other index-related info
uint index; ///< copy of tab->index
#else // in non-debug build, empty class
public:
Plan_change_watchdog(const JOIN_TAB *tab_arg, const bool no_changes_arg) {}
#endif
};
/**
Test if we can skip ordering by using an index.
If the current plan is to use an index that provides ordering, the
plan will not be changed. Otherwise, if an index can be used, the
JOIN_TAB / tab->select struct is changed to use the index.
The index must cover all fields in <order>, or it will not be considered.
@param tab NULL or JOIN_TAB of the accessed table
@param order Linked list of ORDER BY arguments
@param select_limit LIMIT value, or HA_POS_ERROR if no limit
@param no_changes No changes will be made to the query plan.
@param map key_map of applicable indexes.
@param clause_type "ORDER BY" etc for printing in optimizer trace
@todo
- sergeyp: Results of all index merge selects actually are ordered
by clustered PK values.
@note
This function may change tmp_table_param.precomputed_group_by. This
affects how create_tmp_table() treats aggregation functions, so
count_field_types() must be called again to make sure this is taken
into consideration.
@retval
0 We have to use filesort to do the sorting
@retval
1 We can use an index.
*/
static bool
test_if_skip_sort_order(JOIN_TAB *tab, ORDER *order, ha_rows select_limit,
const bool no_changes, const key_map *map,
const char *clause_type)
{
int ref_key;
uint ref_key_parts= 0;
int order_direction= 0;
uint used_key_parts;
TABLE *const table= tab->table();
JOIN *const join= tab->join();
THD *const thd= join->thd;
QUICK_SELECT_I *const save_quick= tab->quick();
int best_key= -1;
bool set_up_ref_access_to_key= false;
bool can_skip_sorting= false; // used as return value
int changed_key= -1;
DBUG_ENTER("test_if_skip_sort_order");
/* Check that we are always called with first non-const table */
assert((uint)tab->idx() == join->const_tables);
Plan_change_watchdog watchdog(tab, no_changes);
/* Sorting a single row can always be skipped */
if (tab->type() == JT_EQ_REF ||
tab->type() == JT_CONST ||
tab->type() == JT_SYSTEM)
{
DBUG_RETURN(1);
}
/*
Check if FT index can be used to retrieve result in the required order.
It is possible if ordering is on the first non-constant table.
*/
if (join->order && join->simple_order)
{
/*
Check if ORDER is DESC, ORDER BY is a single MATCH function.
*/
Item_func_match *ft_func= test_if_ft_index_order(order);
/*
Two possible cases when we can skip sort order:
1. FT_SORTED must be set(Natural mode, no ORDER BY).
2. If FT_SORTED flag is not set then
the engine should support deferred sorting. Deferred sorting means
that sorting is postponed utill the start of index reading(InnoDB).
In this case we set FT_SORTED flag here to let the engine know that
internal sorting is needed.
*/
if (ft_func && ft_func->ft_handler && ft_func->ordered_result())
{
/*
FT index scan is used, so the only additional requirement is
that ORDER BY MATCH function is the same as the function that
is used for FT index.
*/
if (tab->type() == JT_FT &&
ft_func->eq(tab->position()->key->val, true))
{
ft_func->set_hints(join, FT_SORTED, select_limit, false);
DBUG_RETURN(true);
}
/*
No index is used, it's possible to use FT index for ORDER BY if
LIMIT is present and does not exceed count of the records in FT index
and there is no WHERE condition since a condition may potentially
require more rows to be fetch from FT index.
*/
else if (!tab->condition() &&
select_limit != HA_POS_ERROR &&
select_limit <= ft_func->get_count())
{
/* test_if_ft_index_order() always returns master MATCH function. */
assert(!ft_func->master);
/* ref is not set since there is no WHERE condition */
assert(tab->ref().key == -1);
/*Make EXPLAIN happy */
tab->set_type(JT_FT);
tab->ref().key= ft_func->key;
tab->ref().key_parts= 0;
tab->set_index(ft_func->key);
tab->set_ft_func(ft_func);
/* Setup FT handler */
ft_func->set_hints(join, FT_SORTED, select_limit, true);
ft_func->join_key= true;
table->file->ft_handler= ft_func->ft_handler;
DBUG_RETURN(true);
}
}
}
/*
Keys disabled by ALTER TABLE ... DISABLE KEYS should have already
been taken into account.
*/
key_map usable_keys= *map;
for (ORDER *tmp_order=order; tmp_order ; tmp_order=tmp_order->next)
{
Item *item= (*tmp_order->item)->real_item();
if (item->type() != Item::FIELD_ITEM)
{
usable_keys.clear_all();
DBUG_RETURN(0);
}
usable_keys.intersect(((Item_field*) item)->field->part_of_sortkey);
if (usable_keys.is_clear_all())
DBUG_RETURN(0); // No usable keys
}
if (tab->type() == JT_REF_OR_NULL || tab->type() == JT_FT)
DBUG_RETURN(0);
ref_key= -1;
/* Test if constant range in WHERE */
if (tab->type() == JT_REF)
{
assert(tab->ref().key >= 0 && tab->ref().key_parts);
ref_key= tab->ref().key;
ref_key_parts= tab->ref().key_parts;
}
else if (tab->type() == JT_RANGE || tab->type() == JT_INDEX_MERGE)
{
// Range found by opt_range
int quick_type= tab->quick()->get_type();
/*
assume results are not ordered when index merge is used
TODO: sergeyp: Results of all index merge selects actually are ordered
by clustered PK values.
*/
if (quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE ||
quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION ||
quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT)
DBUG_RETURN(0);
ref_key= tab->quick()->index;
ref_key_parts= tab->quick()->used_key_parts;
}
else if (tab->type() == JT_INDEX_SCAN)
{
// The optimizer has decided to use an index scan.
ref_key= tab->index();
ref_key_parts= actual_key_parts(&table->key_info[tab->index()]);
}
Opt_trace_context * const trace= &thd->opt_trace;
Opt_trace_object trace_wrapper(trace);
Opt_trace_object
trace_skip_sort_order(trace, "reconsidering_access_paths_for_index_ordering");
trace_skip_sort_order.add_alnum("clause", clause_type);
Opt_trace_array trace_steps(trace, "steps");
if (ref_key >= 0)
{
/*
We come here when ref/index scan/range scan access has been set
up for this table. Do not change access method if ordering is
provided already.
*/
if (!usable_keys.is_set(ref_key))
{
/*
We come here when ref_key is not among usable_keys, try to find a
usable prefix key of that key.
*/
uint new_ref_key;
/*
If using index only read, only consider other possible index only
keys
*/
if (table->covering_keys.is_set(ref_key))
usable_keys.intersect(table->covering_keys);
if ((new_ref_key= test_if_subkey(order, tab, ref_key, ref_key_parts,
&usable_keys)) < MAX_KEY)
{
/* Found key that can be used to retrieve data in sorted order */
if (tab->ref().key >= 0)
{
/*
We'll use ref access method on key new_ref_key. The actual change
is done further down in this function where we update the plan.
*/
set_up_ref_access_to_key= true;
}
else if (!no_changes)
{
/*
The range optimizer constructed QUICK_RANGE for ref_key, and
we want to use instead new_ref_key as the index. We can't
just change the index of the quick select, because this may
result in an incosistent QUICK_SELECT object. Below we
create a new QUICK_SELECT from scratch so that all its
parameres are set correctly by the range optimizer.
Note that the range optimizer is NOT called if
no_changes==true. This reason is that the range optimizer
cannot find a QUICK that can return ordered result unless
index access (ref or index scan) is also able to do so
(which test_if_order_by_key () will tell).
Admittedly, range access may be much more efficient than
e.g. index scan, but the only thing that matters when
no_change==true is the answer to the question: "Is it
possible to avoid sorting if an index is used to access
this table?". The answer does not depend on the outcome of
the range optimizer.
*/
key_map new_ref_key_map; // Force the creation of quick select
new_ref_key_map.set_bit(new_ref_key); // only for new_ref_key.
Opt_trace_object trace_wrapper(trace);
Opt_trace_object
trace_recest(trace, "rows_estimation");
trace_recest.add_utf8_table(tab->table_ref).
add_utf8("index", table->key_info[new_ref_key].name);
QUICK_SELECT_I *qck;
const bool no_quick=
test_quick_select(thd, new_ref_key_map,
0, // empty table_map
join->calc_found_rows ?
HA_POS_ERROR :
join->unit->select_limit_cnt,
false, // don't force quick range
order->direction, tab,
// we are after make_join_select():
tab->condition(), &tab->needed_reg, &qck,
tab->table()->force_index) <= 0;
assert(tab->quick() == save_quick);
tab->set_quick(qck);
if (no_quick)
{
can_skip_sorting= false;
goto fix_ICP;
}
}
ref_key= new_ref_key;
changed_key= new_ref_key;
}
}
/* Check if we get the rows in requested sorted order by using the key */
if (usable_keys.is_set(ref_key) &&
(order_direction= test_if_order_by_key(order,table,ref_key,
&used_key_parts)))
goto check_reverse_order;
}
{
/*
There is no ref/index scan/range scan access set up for this
table, or it does not provide the requested ordering. Do a
cost-based search on all keys.
*/
uint best_key_parts= 0;
uint saved_best_key_parts= 0;
int best_key_direction= 0;
ha_rows table_records= table->file->stats.records;
/*
If an index scan that cannot provide ordering has been selected
then do not use the index scan key as starting hint to
test_if_cheaper_ordering()
*/
const int ref_key_hint= (order_direction == 0 &&
tab->type() == JT_INDEX_SCAN) ? -1 : ref_key;
/*
Does the query have a "FORCE INDEX [FOR GROUP BY] (idx)" (if
clause is group by) or a "FORCE INDEX [FOR ORDER BY] (idx)" (if
clause is order by)?
*/
const bool is_group_by= join && join->grouped && order == join->group_list;
const bool is_force_index= table->force_index ||
(is_group_by ? table->force_index_group : table->force_index_order);
/*
Find an ordering index alternative over the chosen plan iff
prefer_ordering_index switch is on. This switch is overridden only when
force index for order/group is specified.
*/
if (thd->optimizer_switch_flag(OPTIMIZER_SWITCH_PREFER_ORDERING_INDEX) ||
is_force_index)
test_if_cheaper_ordering(tab, order, table, usable_keys,
ref_key_hint,
select_limit,
&best_key, &best_key_direction,
&select_limit, &best_key_parts,
&saved_best_key_parts);
if (best_key < 0)
{
// No usable key has been found
can_skip_sorting= false;
goto fix_ICP;
}
/*
filesort() and join cache are usually faster than reading in
index order and not using join cache. Don't use index scan
unless:
- the user specified FORCE INDEX [FOR {GROUP|ORDER} BY] (have to assume
the user knows what's best)
- the chosen index is clustered primary key (table scan is not cheaper)
*/
if (!is_force_index &&
(select_limit >= table_records) &&
(tab->type() == JT_ALL &&
join->primary_tables > join->const_tables + 1) &&
((unsigned) best_key != table->s->primary_key ||
!table->file->primary_key_is_clustered()))
{
can_skip_sorting= false;
goto fix_ICP;
}
if (table->quick_keys.is_set(best_key) &&
!tab->quick_order_tested.is_set(best_key) &&
best_key != ref_key)
{
tab->quick_order_tested.set_bit(best_key);
Opt_trace_object trace_wrapper(trace);
Opt_trace_object
trace_recest(trace, "rows_estimation");
trace_recest.add_utf8_table(tab->table_ref).
add_utf8("index", table->key_info[best_key].name);
key_map keys_to_use; // Force the creation of quick select
keys_to_use.set_bit(best_key); // only best_key.
QUICK_SELECT_I *qck;
test_quick_select(thd,
keys_to_use,
0, // empty table_map
join->calc_found_rows ?
HA_POS_ERROR :
join->unit->select_limit_cnt,
true, // force quick range
order->direction, tab, tab->condition(),
&tab->needed_reg, &qck, tab->table()->force_index);
/*
If tab->quick() pointed to another quick than save_quick, we would
lose access to it and leak memory.
*/
assert(tab->quick() == save_quick || tab->quick() == NULL);
tab->set_quick(qck);
}
order_direction= best_key_direction;
/*
saved_best_key_parts is actual number of used keyparts found by the
test_if_order_by_key function. It could differ from keyinfo->key_parts,
thus we have to restore it in case of desc order as it affects
QUICK_SELECT_DESC behaviour.
*/
used_key_parts= (order_direction == -1) ?
saved_best_key_parts : best_key_parts;
changed_key= best_key;
// We will use index scan or range scan:
set_up_ref_access_to_key= false;
}
check_reverse_order:
assert(order_direction != 0);
if (order_direction == -1) // If ORDER BY ... DESC
{
if (tab->quick())
{
/*
Don't reverse the sort order, if it's already done.
(In some cases test_if_order_by_key() can be called multiple times
*/
if (tab->quick()->reverse_sorted())
{
can_skip_sorting= true;
goto fix_ICP;
}
if (tab->quick()->reverse_sort_possible())
can_skip_sorting= true;
else
{
can_skip_sorting= false;
goto fix_ICP;
}
}
else
{
// Other index access (ref or scan) poses no problem
can_skip_sorting= true;
}
}
else
{
// ORDER BY ASC poses no problem
can_skip_sorting= true;
}
assert(can_skip_sorting);
/*
Update query plan with access pattern for doing
ordered access according to what we have decided
above.
*/
if (!no_changes) // We are allowed to update QEP
{
if (set_up_ref_access_to_key)
{
/*
We'll use ref access method on key changed_key. In general case
the index search tuple for changed_ref_key will be different (e.g.
when one index is defined as (part1, part2, ...) and another as
(part1, part2(N), ...) and the WHERE clause contains
"part1 = const1 AND part2=const2".
So we build tab->ref() from scratch here.
*/
Key_use *keyuse= tab->keyuse();
while (keyuse->key != (uint)changed_key &&
keyuse->table_ref == tab->table_ref)
keyuse++;
if (create_ref_for_key(join, tab, keyuse, tab->prefix_tables()))
{
can_skip_sorting= false;
goto fix_ICP;
}
assert(tab->type() != JT_REF_OR_NULL && tab->type() != JT_FT);
// Changing the key makes filter_effect obsolete
tab->position()->filter_effect= COND_FILTER_STALE;
}
else if (best_key >= 0)
{
/*
If ref_key used index tree reading only ('Using index' in EXPLAIN),
and best_key doesn't, then revert the decision.
*/
if(!table->covering_keys.is_set(best_key))
table->set_keyread(false);
if (!tab->quick() || tab->quick() == save_quick) // created no QUICK
{
// Avoid memory leak:
assert(tab->quick() == save_quick || tab->quick() == NULL);
tab->set_quick(NULL);
tab->set_index(best_key);
tab->set_type(JT_INDEX_SCAN); // Read with index_first(), index_next()
/*
There is a bug. When we change here, e.g. from group_min_max to
index scan: loose index scan expected to read a small number of rows
(jumping through the index), this small number was in
position()->rows_fetched; index scan will read much more, so
rows_fetched should be updated. So should the filtering effect.
It is visible in main.distinct in trunk:
explain SELECT distinct a from t3 order by a desc limit 2;
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t3 NULL index a a 5 NULL 40 25.00 Using index
"rows=40" should be ~200 i.e. # of records in table. Filter should be
100.00 (no WHERE).
*/
table->file->ha_index_or_rnd_end();
if (thd->lex->is_explain())
{
/*
@todo this neutralizes add_ref_to_table_cond(); as a result
EXPLAIN shows no "using where" though real SELECT has one.
*/
tab->ref().key= -1;
tab->ref().key_parts= 0;
}
tab->position()->filter_effect= COND_FILTER_STALE;
}
else if (tab->type() != JT_ALL)
{
/*
We're about to use a quick access to the table.
We need to change the access method so as the quick access
method is actually used.
*/
assert(tab->quick());
assert(tab->quick()->index==(uint)best_key);
tab->set_type(calc_join_type(tab->quick()->get_type()));
tab->use_quick=QS_RANGE;
tab->ref().key= -1;
tab->ref().key_parts=0; // Don't use ref key.
if (tab->quick()->is_loose_index_scan())
join->tmp_table_param.precomputed_group_by= TRUE;
tab->position()->filter_effect= COND_FILTER_STALE;
}
} // best_key >= 0
if (order_direction == -1) // If ORDER BY ... DESC
{
if (tab->quick())
{
/* ORDER BY range_key DESC */
QUICK_SELECT_I *tmp= tab->quick()->make_reverse(used_key_parts);
if (!tmp)
{
/* purecov: begin inspected */
can_skip_sorting= false; // Reverse sort failed -> filesort
goto fix_ICP;
/* purecov: end */
}
if (tab->quick() != tmp && tab->quick() != save_quick)
delete tab->quick();
tab->set_quick(tmp);
tab->set_type(calc_join_type(tmp->get_type()));
tab->position()->filter_effect= COND_FILTER_STALE;
}
else if (tab->type() == JT_REF &&
tab->ref().key_parts <= used_key_parts)
{
/*
SELECT * FROM t1 WHERE a=1 ORDER BY a DESC,b DESC
Use a traversal function that starts by reading the last row
with key part (A) and then traverse the index backwards.
*/
tab->reversed_access= true;
/*
The current implementation of join_read_prev_same() does not
work well in combination with ICP and can lead to increased
execution time. Setting changed_key to the current key
(based on that we change the access order for the key) will
ensure that a pushed index condition will be cancelled.
*/
changed_key= tab->ref().key;
}
else if (tab->type() == JT_INDEX_SCAN)
tab->reversed_access= true;
}
else if (tab->quick())
tab->quick()->need_sorted_output();
} // QEP has been modified
fix_ICP:
/*
Cleanup:
We may have both a 'tab->quick()' and 'save_quick' (original)
at this point. Delete the one that we won't use.
*/
if (can_skip_sorting && !no_changes)
{
if (tab->type() == JT_INDEX_SCAN &&
select_limit < table->file->stats.records)
{
tab->position()->rows_fetched= select_limit;
tab->position()->filter_effect= COND_FILTER_STALE_NO_CONST;
}
// Keep current (ordered) tab->quick()
if (save_quick != tab->quick())
delete save_quick;
}
else
{
// Restore original save_quick
if (tab->quick() != save_quick)
{
delete tab->quick();
tab->set_quick(save_quick);
}
}
trace_steps.end();
Opt_trace_object
trace_change_index(trace, "index_order_summary");
trace_change_index.add_utf8_table(tab->table_ref)
.add("index_provides_order", can_skip_sorting)
.add_alnum("order_direction", order_direction == 1 ? "asc" :
((order_direction == -1) ? "desc" :
"undefined"));
if (changed_key >= 0)
{
// switching to another index
// Should be no pushed conditions at this point
assert(!table->file->pushed_idx_cond);
if (unlikely(trace->is_started()))
{
trace_change_index.add_utf8("index", table->key_info[changed_key].name);
trace_change_index.add("plan_changed", !no_changes);
if (!no_changes)
trace_change_index.add_alnum("access_type", join_type_str[tab->type()]);
}
}
else if (unlikely(trace->is_started()))
{
trace_change_index.add_utf8("index",
ref_key >= 0 ?
table->key_info[ref_key].name : "unknown");
trace_change_index.add("plan_changed", false);
}
DBUG_RETURN(can_skip_sorting);
}
/**
Prune partitions for all tables of a join (query block).
Requires that tables have been locked.
@returns false if success, true if error
*/
bool JOIN::prune_table_partitions()
{
assert(select_lex->partitioned_table_count);
for (TABLE_LIST *tbl= select_lex->leaf_tables; tbl; tbl= tbl->next_leaf)
{
/*
If tbl->embedding!=NULL that means that this table is in the inner
part of the nested outer join, and we can't do partition pruning
(TODO: check if this limitation can be lifted.
This also excludes semi-joins. Is that intentional?)
This will try to prune non-static conditions, which can
be used after the tables are locked.
*/
if (!tbl->embedding)
{
Item *prune_cond= tbl->join_cond_optim() ?
tbl->join_cond_optim() : where_cond;
if (prune_partitions(thd, tbl->table, prune_cond))
return true;
}
}
return false;
}
/**
A helper function to check whether it's better to use range than ref.
@details
Heuristic: Switch from 'ref' to 'range' access if 'range'
access can utilize more keyparts than 'ref' access. Conditions
for doing switching:
1) Range access is possible Or tab->dodgy_ref_cost is set.
2) This function is not relevant for FT, since there is no range access for
that type of index.
3) Used parts of key shouldn't have nullable parts & ref_or_null isn't used.
4) 'ref' access depends on a constant, not a value read from a
table earlier in the join sequence.
Rationale: if 'ref' depends on a value from another table,
the join condition is not used to limit the rows read by
'range' access (that would require dynamic range - 'Range
checked for each record'). In other words, if 'ref' depends
on a value from another table, we have a query with
conditions of the form
this_table.idx_col1 = other_table.col AND <<- used by 'ref'
this_table.idx_col1 OP <const> AND <<- used by 'range'
this_table.idx_col2 OP <const> AND ... <<- used by 'range'
and an index on (idx_col1,idx_col2,...). But the fact that
'range' access uses more keyparts does not mean that it is
more selective than 'ref' access because these access types
utilize different parts of the query condition. We
therefore trust the cost based choice made by
best_access_path() instead of forcing a heuristic choice
here.
5a) 'ref' access and 'range' access uses the same index.
5b) 'range' access uses more keyparts than 'ref' access.
OR
6) Ref has borrowed the index estimate from range and created a cost
estimate (See Optimize_table_order::find_best_ref). This will be a
problem if range built it's row estimate using a larger number of key
parts than ref. In such a case, shift to range access over the same
index. So run the range optimizer with that index as the only choice.
(Condition 5 is not relevant here since it has been tested in
find_best_ref.)
@param thd THD To re-run range optimizer.
@param tab JOIN_TAB To check the above conditions.
@return true Range is better than ref
@return false Ref is better or switch isn't possible
@todo: This decision should rather be made in best_access_path()
*/
static bool can_switch_from_ref_to_range(THD *thd, JOIN_TAB *tab)
{
if ((tab->quick() || tab->dodgy_ref_cost) && // 1)
tab->position()->key->keypart != FT_KEYPART) // 2)
{
uint keyparts= 0, length= 0;
table_map dep_map= 0;
bool maybe_null= false;
calc_length_and_keyparts(tab->position()->key, tab,
tab->position()->key->key,
tab->prefix_tables(), NULL, &length, &keyparts,
&dep_map, &maybe_null);
if (maybe_null || // 3)
dep_map) // 4)
return false;
if (tab->quick() &&
tab->position()->key->key == tab->quick()->index) // 5a)
return length < tab->quick()->max_used_key_length; // 5b)
else if (tab->dodgy_ref_cost) // 6)
{
key_map new_ref_key_map;
new_ref_key_map.set_bit(tab->position()->key->key);
Opt_trace_context * const trace= &thd->opt_trace;
Opt_trace_object trace_wrapper(trace);
Opt_trace_object
can_switch(trace, "check_if_range_uses_more_keyparts_than_ref");
Opt_trace_object
trace_setup_cond(trace, "rerunning_range_optimizer_for_single_index");
QUICK_SELECT_I *qck;
if (test_quick_select(thd, new_ref_key_map,
0, // empty table_map
tab->join()->row_limit,
false, // don't force quick range
ORDER::ORDER_NOT_RELEVANT,
tab,
tab->join_cond() ? tab->join_cond() :
tab->join()->where_cond,
&tab->needed_reg,
&qck, true) > 0)
{
if (length < qck->max_used_key_length)
{
delete tab->quick();
tab->set_quick(qck);
return true;
}
else
{
Opt_trace_object (trace, "access_type_unchanged").
add("ref_key_length", length).
add("range_key_length", qck->max_used_key_length);
delete qck;
}
}
}
}
return false;
}
/**
An utility function - apply heuristics and optimize access methods to tables.
Currently this function can change REF to RANGE and ALL to INDEX scan if
latter is considered to be better (not cost-based) than the former.
@note Side effect - this function could set 'Impossible WHERE' zero
result.
*/
void JOIN::adjust_access_methods()
{
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
for (uint i= const_tables; i < tables; i++)
{
JOIN_TAB *const tab= best_ref[i];
TABLE_LIST *const tl= tab->table_ref;
if (tab->type() == JT_ALL)
{
/*
It's possible to speedup query by switching from full table scan to
the scan of covering index, due to less data being read.
Prerequisites for this are:
1) Keyread (i.e index only scan) is allowed (table isn't updated/deleted
from)
2) Covering indexes are available
3) This isn't a derived table/materialized view
*/
if (!tab->table()->no_keyread && // 1
!tab->table()->covering_keys.is_clear_all() && // 2
!tl->uses_materialization()) // 3
{
/*
It has turned out that the change commented out below, while speeding
things up for disk-bound loads, slows them down for cases when the data
is in disk cache (see BUG#35850):
// See bug #26447: "Using the clustered index for a table scan
// is always faster than using a secondary index".
if (table->s->primary_key != MAX_KEY &&
table->file->primary_key_is_clustered())
tab->index= table->s->primary_key;
else
tab->index=find_shortest_key(table, & table->covering_keys);
*/
if (tab->position()->sj_strategy != SJ_OPT_LOOSE_SCAN)
tab->set_index(find_shortest_key(tab->table(), &tab->table()->covering_keys));
tab->set_type(JT_INDEX_SCAN); // Read with index_first / index_next
// From table scan to index scan, thus filter effect needs no recalc.
}
}
else if (tab->type() == JT_REF)
{
if (can_switch_from_ref_to_range(thd, tab))
{
tab->set_type(JT_RANGE);
Opt_trace_context * const trace= &thd->opt_trace;
Opt_trace_object wrapper(trace);
Opt_trace_object (trace, "access_type_changed").
add_utf8_table(tl).
add_utf8("index",
tab->table()->key_info[tab->position()->key->key].name).
add_alnum("old_type", "ref").
add_alnum("new_type", join_type_str[tab->type()]).
add_alnum("cause", "uses_more_keyparts");
tab->use_quick= QS_RANGE;
tab->position()->filter_effect= COND_FILTER_STALE;
}
else
{
// Cleanup quick, REF/REF_OR_NULL/EQ_REF, will be clarified later
delete tab->quick();
tab->set_quick(NULL);
}
}
// Ensure AM consistency
assert(!(tab->quick() && (tab->type() == JT_REF || tab->type() == JT_ALL)));
assert((tab->type() != JT_RANGE && tab->type() != JT_INDEX_MERGE) ||
tab->quick());
if (!tab->const_keys.is_clear_all() &&
tab->table()->reginfo.impossible_range &&
((i == const_tables && tab->type() == JT_REF) ||
((tab->type() == JT_ALL || tab->type() == JT_RANGE ||
tab->type() == JT_INDEX_MERGE || tab->type() == JT_INDEX_SCAN) &&
tab->use_quick != QS_RANGE)) &&
!tab->table_ref->is_inner_table_of_outer_join())
zero_result_cause=
"Impossible WHERE noticed after reading const tables";
}
}
static JOIN_TAB *alloc_jtab_array(THD *thd, uint table_count)
{
JOIN_TAB *t= new (thd->mem_root) JOIN_TAB[table_count];
if (!t)
return NULL; /* purecov: inspected */
QEP_shared *qs= new (thd->mem_root) QEP_shared[table_count];
if (!qs)
return NULL; /* purecov: inspected */
for (uint i= 0; i < table_count; ++i)
t[i].set_qs(qs++);
return t;
}
/**
Set up JOIN_TAB structs according to the picked join order in best_positions.
This allocates execution structures so may be called only after we have the
very final plan. It must be called after
Optimize_table_order::fix_semijoin_strategies().
@return False if success, True if error
@details
- create join->join_tab array and copy from existing JOIN_TABs in join order
- create helper structs for materialized semi-join handling
- finalize semi-join strategy choices
- Number of intermediate tables "tmp_tables" is calculated.
- "tables" and "primary_tables" are recalculated.
- for full and index scans info of estimated # of records is updated.
- in a helper function:
- all heuristics are applied and the final access method type is picked
for each join_tab (only test_if_skip_sortorder() could override it)
- AM consistency is ensured (e.g only range and index merge are allowed
to have quick select set).
- if "Impossible WHERE" is detected - appropriate zero_result_cause is
set.
Notice that intermediate tables will not have a POSITION reference; and they
will not have a TABLE reference before the final stages of code generation.
@todo the block which sets tab->type should move to adjust_access_methods
for unification.
*/
bool JOIN::get_best_combination()
{
DBUG_ENTER("JOIN::get_best_combination");
// At this point "tables" and "primary"tables" represent the same:
assert(tables == primary_tables);
/*
Allocate additional space for tmp tables.
Number of plan nodes:
# of regular input tables (including semi-joined ones) +
# of semi-join nests for materialization +
1? + // For GROUP BY
1? + // For DISTINCT
1? + // For aggregation functions aggregated in outer query
// when used with distinct
1? + // For ORDER BY
1? // buffer result
Up to 2 tmp tables are actually used, but it's hard to tell exact number
at this stage.
*/
uint num_tmp_tables= (group_list ? 1 : 0) +
(select_distinct ?
(tmp_table_param.outer_sum_func_count ? 2 : 1) : 0) +
(order ? 1 : 0) +
(select_lex->active_options() &
(SELECT_BIG_RESULT | OPTION_BUFFER_RESULT) ? 1 : 0);
if (num_tmp_tables > 2)
num_tmp_tables= 2;
/*
Rearrange queries with materialized semi-join nests so that the semi-join
nest is replaced with a reference to a materialized temporary table and all
materialized subquery tables are placed after the intermediate tables.
After the following loop, "inner_target" is the position of the first
subquery table (if any). "outer_target" is the position of first outer
table, and will later be used to track the position of any materialized
temporary tables.
*/
const bool has_semijoin= !select_lex->sj_nests.is_empty();
uint outer_target= 0;
uint inner_target= primary_tables + num_tmp_tables;
uint sjm_nests= 0;
if (has_semijoin)
{
for (uint tableno= 0; tableno < primary_tables; )
{
if (sj_is_materialize_strategy(best_positions[tableno].sj_strategy))
{
sjm_nests++;
inner_target-= (best_positions[tableno].n_sj_tables - 1);
tableno+= best_positions[tableno].n_sj_tables;
}
else
tableno++;
}
}
JOIN_TAB *tmp_join_tabs= NULL;
if (sjm_nests + num_tmp_tables)
{
// join_tab array only has "primary_tables" tables. We need those more:
if (!(tmp_join_tabs= alloc_jtab_array(thd, sjm_nests + num_tmp_tables)))
DBUG_RETURN(true); /* purecov: inspected */
}
// To check that we fill the array correctly: fill it with zeros first
memset(best_ref, 0, sizeof(JOIN_TAB*) * (primary_tables + sjm_nests +
num_tmp_tables));
int sjm_index= tables; // Number assigned to materialized temporary table
int remaining_sjm_inner= 0;
bool err= false;
for (uint tableno= 0; tableno < tables; tableno++)
{
POSITION *const pos= best_positions + tableno;
if (has_semijoin && sj_is_materialize_strategy(pos->sj_strategy))
{
assert(outer_target < inner_target);
TABLE_LIST *const sj_nest= pos->table->emb_sj_nest;
// Handle this many inner tables of materialized semi-join
remaining_sjm_inner= pos->n_sj_tables;
/*
If we fail in some allocation below, we cannot bail out immediately;
that would put us in a difficult situation to clean up; imagine we
have planned this layout:
outer1 - sj_mat_tmp1 - outer2 - sj_mat_tmp2 - outer3
We have successfully filled a JOIN_TAB for sj_mat_tmp1, and are
failing to fill a JOIN_TAB for sj_mat_tmp2 (OOM). So we want to quit
this function, which will lead to cleanup functions.
But sj_mat_tmp1 is in this->best_ref only, outer3 is in this->join_tab
only: what is the array to traverse for cleaning up? What is the
number of tables to loop over?
So: if we fail in the present loop, we record the error but continue
filling best_ref; when it's fully filled, bail out, because then
best_ref can be used as reliable array for cleaning up.
*/
JOIN_TAB *const tab= tmp_join_tabs++;
best_ref[outer_target]= tab;
tab->set_join(this);
tab->set_idx(outer_target);
/*
Up to this point there cannot be a failure. JOIN_TAB has been filled
enough to be clean-able.
*/
Semijoin_mat_exec *const sjm_exec=
new (thd->mem_root)
Semijoin_mat_exec(sj_nest,
(pos->sj_strategy == SJ_OPT_MATERIALIZE_SCAN),
remaining_sjm_inner, outer_target, inner_target);
tab->set_sj_mat_exec(sjm_exec);
if (!sjm_exec ||
setup_semijoin_materialized_table(tab, sjm_index,
pos, best_positions + sjm_index))
err= true; /* purecov: inspected */
outer_target++;
sjm_index++;
}
/*
Locate join_tab target for the table we are considering.
(remaining_sjm_inner becomes negative for non-SJM tables, this can be
safely ignored).
*/
const uint target=
(remaining_sjm_inner--) > 0 ? inner_target++ : outer_target++;
JOIN_TAB *const tab= pos->table;
best_ref[target]= tab;
tab->set_idx(target);
tab->set_position(pos);
TABLE *const table= tab->table();
if (tab->type() != JT_CONST && tab->type() != JT_SYSTEM)
{
if (pos->sj_strategy == SJ_OPT_LOOSE_SCAN && tab->quick() &&
tab->quick()->index != pos->loosescan_key)
{
/*
We must use the duplicate-eliminating index, so this QUICK is not
an option.
*/
delete tab->quick();
tab->set_quick(NULL);
}
if (!pos->key)
{
if (tab->quick())
tab->set_type(calc_join_type(tab->quick()->get_type()));
else
tab->set_type(JT_ALL);
}
else
// REF or RANGE, clarify later when prefix tables are set for JOIN_TABs
tab->set_type(JT_REF);
}
assert(tab->type() != JT_UNKNOWN);
assert(table->reginfo.join_tab == tab);
if (!tab->join_cond())
table->reginfo.not_exists_optimize= false; // Only with LEFT JOIN
map2table[tab->table_ref->tableno()]= tab;
}
// Count the materialized semi-join tables as regular input tables
tables+= sjm_nests + num_tmp_tables;
// Set the number of non-materialized tables:
primary_tables= outer_target;
/*
Between the last outer table or sj-mat tmp table, and the first sj-mat
inner table, there may be 2 slots for sort/group/etc tmp tables:
*/
for (uint i= 0; i < num_tmp_tables; ++i)
{
const uint idx= outer_target + i;
tmp_join_tabs->set_join(this);
tmp_join_tabs->set_idx(idx);
assert(best_ref[idx] == NULL); // verify that not overwriting
best_ref[idx]= tmp_join_tabs++;
/*
note that set_table() cannot be called yet. We may not even use this
JOIN_TAB in the end, it's dummy at the moment. Which can be tested with
"position()!=NULL".
*/
}
// make array unreachable: should walk JOIN_TABs by best_ref now
join_tab= NULL;
if (err)
DBUG_RETURN(true); /* purecov: inspected */
if (has_semijoin)
{
set_semijoin_info();
// Update equalities and keyuses after having added SJ materialization
if (update_equalities_for_sjm())
DBUG_RETURN(true);
}
if (!plan_is_const())
{
// Assign map of "available" tables to all tables belonging to query block
set_prefix_tables();
adjust_access_methods();
}
// Calculate outer join info
if (select_lex->outer_join)
make_outerjoin_info();
// sjm is no longer needed, trash it. To reuse it, reset its members!
List_iterator<TABLE_LIST> sj_list_it(select_lex->sj_nests);
TABLE_LIST *sj_nest;
while ((sj_nest= sj_list_it++))
TRASH(&sj_nest->nested_join->sjm, sizeof(sj_nest->nested_join->sjm));
DBUG_RETURN(false);
}
/*
Revise usage of join buffer for the specified table and the whole nest
SYNOPSIS
revise_cache_usage()
tab join table for which join buffer usage is to be revised
DESCRIPTION
The function revise the decision to use a join buffer for the table 'tab'.
If this table happened to be among the inner tables of a nested outer join/
semi-join the functions denies usage of join buffers for all of them
RETURN
none
*/
static
void revise_cache_usage(JOIN_TAB *join_tab)
{
plan_idx first_inner= join_tab->first_inner();
JOIN *const join= join_tab->join();
if (first_inner != NO_PLAN_IDX)
{
plan_idx end_tab= join_tab->idx();
for (first_inner= join_tab->first_inner();
first_inner != NO_PLAN_IDX;
first_inner= join->best_ref[first_inner]->first_upper())
{
for (plan_idx i= end_tab-1; i >= first_inner; --i)
join->best_ref[i]->set_use_join_cache(JOIN_CACHE::ALG_NONE);
end_tab= first_inner;
}
}
else if (join_tab->get_sj_strategy() == SJ_OPT_FIRST_MATCH)
{
plan_idx first_sj_inner= join_tab->first_sj_inner();
for (plan_idx i= join_tab->idx()-1; i >= first_sj_inner; --i)
{
JOIN_TAB *tab= join->best_ref[i];
if (tab->first_sj_inner() == first_sj_inner)
tab->set_use_join_cache(JOIN_CACHE::ALG_NONE);
}
}
else
join_tab->set_use_join_cache(JOIN_CACHE::ALG_NONE);
assert(join->qep_tab == NULL);
}
/**
Set up join buffering for a specified table, if possible.
@param tab joined table to check join buffer usage for
@param join join for which the check is performed
@param no_jbuf_after don't use join buffering after table with this number
@return false if successful, true if error.
Currently, allocation errors for join cache objects are ignored,
and regular execution is chosen silently.
@details
The function finds out whether the table 'tab' can be joined using a join
buffer. This check is performed after the best execution plan for 'join'
has been chosen. If the function decides that a join buffer can be employed
then it selects the most appropriate join cache type, which later will
be instantiated by init_join_cache().
If it has already been decided to not use join buffering for this table,
no action is taken.
Often it is already decided that join buffering will be used earlier in
the optimization process, and this will also ensure that the most correct
cost for the operation is calculated, and hence the probability of
choosing an optimal join plan is higher. However, some join buffering
decisions cannot currently be taken before this stage, hence we need this
function to decide the most accurate join buffering strategy.
@todo Long-term it is the goal that join buffering strategy is decided
when the plan is selected.
The result of the check and the type of the join buffer to be used
depend on:
- the access method to access rows of the joined table
- whether the join table is an inner table of an outer join or semi-join
- the optimizer_switch settings for join buffering
- the join 'options'.
In any case join buffer is not used if the number of the joined table is
greater than 'no_jbuf_after'.
If block_nested_loop is turned on, and if all other criteria for using
join buffering is fulfilled (see below), then join buffer is used
for any join operation (inner join, outer join, semi-join) with 'JT_ALL'
access method. In that case, a JOIN_CACHE_BNL type is always employed.
If an index is used to access rows of the joined table and batched_key_access
is on, then a JOIN_CACHE_BKA type is employed. (Unless debug flag,
test_bka unique, is set, then a JOIN_CACHE_BKA_UNIQUE type is employed
instead.)
If the function decides that a join buffer can be used to join the table
'tab' then it sets @c tab->use_join_cache to reflect the chosen algorithm.
@note
For a nested outer join/semi-join, currently, we either use join buffers for
all inner tables or for none of them.
@todo
Support BKA inside SJ-Materialization nests. When doing this, we'll need
to only store sj-inner tables in the join buffer.
#if 0
JOIN_TAB *first_tab= join->join_tab+join->const_tables;
uint n_tables= i-join->const_tables;
/ *
We normally put all preceding tables into the join buffer, except
for the constant tables.
If we're inside a semi-join materialization nest, e.g.
outer_tbl1 outer_tbl2 ( inner_tbl1, inner_tbl2 ) ...
^-- we're here
then we need to put into the join buffer only the tables from
within the nest.
* /
if (i >= first_sjm_table && i < last_sjm_table)
{
n_tables= i - first_sjm_table; // will be >0 if we got here
first_tab= join->join_tab + first_sjm_table;
}
#endif
*/
static bool setup_join_buffering(JOIN_TAB *tab, JOIN *join, uint no_jbuf_after)
{
ASSERT_BEST_REF_IN_JOIN_ORDER(join);
Cost_estimate cost;
ha_rows rows;
uint bufsz= 4096;
uint join_cache_flags = 0;
const bool bnl_on= hint_table_state(join->thd, tab->table_ref->table,
BNL_HINT_ENUM, OPTIMIZER_SWITCH_BNL);
const bool bka_on= hint_table_state(join->thd, tab->table_ref->table,
BKA_HINT_ENUM, OPTIMIZER_SWITCH_BKA);
const uint tableno= tab->idx();
const uint tab_sj_strategy= tab->get_sj_strategy();
bool use_bka_unique= false;
DBUG_EXECUTE_IF("test_bka_unique", use_bka_unique= true;);
/*
If all key_parts are null_rejecting, the MultiRangeRowIterator will
eliminate all NULL values in the key set, such that
HA_MRR_NO_NULL_ENDPOINTS can be promised.
*/
const key_part_map keypart_map = make_prev_keypart_map(tab->ref().key_parts);
if (tab->ref().null_rejecting == keypart_map) {
join_cache_flags |= HA_MRR_NO_NULL_ENDPOINTS;
}
// Set preliminary join cache setting based on decision from greedy search
tab->set_use_join_cache(tab->position()->use_join_buffer ?
JOIN_CACHE::ALG_BNL : JOIN_CACHE::ALG_NONE);
if (tableno == join->const_tables)
{
assert(tab->use_join_cache() == JOIN_CACHE::ALG_NONE);
return false;
}
if (!(bnl_on || bka_on))
goto no_join_cache;
/*
psergey-todo: why the below when execution code seems to handle the
"range checked for each record" case?
*/
if (tab->use_quick == QS_DYNAMIC_RANGE)
goto no_join_cache;
/* No join buffering if prevented by no_jbuf_after */
if (tableno > no_jbuf_after)
goto no_join_cache;
/*
An inner table of an outer join nest must not use join buffering if
the first inner table of that outer join nest does not use join buffering.
This condition is not handled by earlier optimizer stages.
*/
if (tab->first_inner() != NO_PLAN_IDX &&
tab->first_inner() != tab->idx() &&
!join->best_ref[tab->first_inner()]->use_join_cache())
goto no_join_cache;
/*
The first inner table of an outer join nest must not use join buffering
if the tables in the embedding outer join nest do not use join buffering.
This condition is not handled by earlier optimizer stages.
*/
if (tab->first_upper() != NO_PLAN_IDX &&
!join->best_ref[tab->first_upper()]->use_join_cache())
goto no_join_cache;
switch (tab_sj_strategy)
{
case SJ_OPT_FIRST_MATCH:
/*
Use join cache with FirstMatch semi-join strategy only when semi-join
contains only one table.
*/
if (!tab->is_single_inner_of_semi_join())
{
assert(tab->use_join_cache() == JOIN_CACHE::ALG_NONE);
goto no_join_cache;
}
break;
case SJ_OPT_LOOSE_SCAN:
/* No join buffering if this semijoin nest is handled by loosescan */
assert(tab->use_join_cache() == JOIN_CACHE::ALG_NONE);
goto no_join_cache;
case SJ_OPT_MATERIALIZE_LOOKUP:
case SJ_OPT_MATERIALIZE_SCAN:
/*
The Materialize strategies reuse the join_tab belonging to the
first table that was materialized. Neither table can use join buffering:
- The first table in a join never uses join buffering.
- The join_tab used for looking up a row in the materialized table, or
scanning the rows of a materialized table, cannot use join buffering.
We allow join buffering for the remaining tables of the materialized
semi-join nest.
*/
if (tab->first_sj_inner() == tab->idx())
{
assert(tab->use_join_cache() == JOIN_CACHE::ALG_NONE);
goto no_join_cache;
}
break;
case SJ_OPT_DUPS_WEEDOUT:
// This strategy allows the same join buffering as a regular join would.
case SJ_OPT_NONE:
break;
}
/*
The following code prevents use of join buffering when there is an
outer join operation and first match semi-join strategy is used, because:
Outer join needs a "match flag" to track that a row should be
NULL-complemented, such flag being attached to first inner table's cache
(tracks whether the cached row from outer table got a match, in which case
no NULL-complemented row is needed).
FirstMatch also needs a "match flag", such flag is attached to sj inner
table's cache (tracks whether the cached row from outer table already got
a first match in the sj-inner table, in which case we don't need to join
this cached row again)
- but a row in a cache has only one "match flag"
- so if "sj inner table"=="first inner", there is a problem.
*/
if (tab_sj_strategy == SJ_OPT_FIRST_MATCH &&
tab->is_inner_table_of_outer_join())
goto no_join_cache;
switch (tab->type()) {
case JT_ALL:
case JT_INDEX_SCAN:
case JT_RANGE:
case JT_INDEX_MERGE:
if (!bnl_on)
{
assert(tab->use_join_cache() == JOIN_CACHE::ALG_NONE);
goto no_join_cache;
}
tab->set_use_join_cache(JOIN_CACHE::ALG_BNL);
return false;
case JT_SYSTEM:
case JT_CONST:
case JT_REF:
case JT_EQ_REF:
if (!bka_on)
{
assert(tab->use_join_cache() == JOIN_CACHE::ALG_NONE);
goto no_join_cache;
}
/*
Disable BKA for materializable derived tables/views as they aren't
instantiated yet.
*/
if (tab->table_ref->uses_materialization())
goto no_join_cache;
/*
Can't use BKA for subquery if dealing with a subquery that can
turn a ref access into a "full scan on NULL key" table scan.
@see Item_in_optimizer::val_int()
@see subselect_single_select_engine::exec()
@see TABLE_REF::cond_guards
@see push_index_cond()
@todo: This choice to not use BKA should be done before making
cost estimates, e.g. in set_join_buffer_properties(). That
happens before cond guards are set up, so instead of doing the
check below, BKA should be disabled if
- We are in an IN subquery, and
- The IN predicate is not a top_level_item, and
- The left_expr of the IN predicate may contain NULL values
(left_expr->maybe_null)
*/
if (tab->has_guarded_conds())
goto no_join_cache;
if (tab->table()->covering_keys.is_set(tab->ref().key))
join_cache_flags|= HA_MRR_INDEX_ONLY;
rows= tab->table()->file->multi_range_read_info(tab->ref().key, 10, 20,
&bufsz,
&join_cache_flags, &cost);
/*
Cannot use BKA/BKA_UNIQUE if
1. MRR scan cannot be performed, or
2. MRR default implementation is used
Cannot use BKA if
3. HA_MRR_NO_ASSOCIATION flag is set
*/
if ((rows == HA_POS_ERROR) || // 1
(join_cache_flags & HA_MRR_USE_DEFAULT_IMPL) || // 2
((join_cache_flags & HA_MRR_NO_ASSOCIATION) && // 3
!use_bka_unique))
goto no_join_cache;
if (use_bka_unique)
tab->set_use_join_cache(JOIN_CACHE::ALG_BKA_UNIQUE);
else
tab->set_use_join_cache(JOIN_CACHE::ALG_BKA);
tab->join_cache_flags= join_cache_flags;
return false;
default : ;
}
no_join_cache:
revise_cache_usage(tab);
tab->set_use_join_cache(JOIN_CACHE::ALG_NONE);
return false;
}
/*****************************************************************************
Make some simple condition optimization:
If there is a test 'field = const' change all refs to 'field' to 'const'
Remove all dummy tests 'item = item', 'const op const'.
Remove all 'item is NULL', when item can never be null!
item->marker should be 0 for all items on entry
Return in cond_value FALSE if condition is impossible (1 = 2)
*****************************************************************************/
class COND_CMP :public ilink<COND_CMP> {
public:
static void *operator new(size_t size)
{
return sql_alloc(size);
}
static void operator delete(void *ptr MY_ATTRIBUTE((unused)),
size_t size MY_ATTRIBUTE((unused)))
{ TRASH(ptr, size); }
Item *and_level;
Item_func *cmp_func;
COND_CMP(Item *a,Item_func *b) :and_level(a),cmp_func(b) {}
};
/**
Find the multiple equality predicate containing a field.
The function retrieves the multiple equalities accessed through
the cond_equal structure from current level and up looking for
an equality containing a field. It stops retrieval as soon as the equality
is found and set up inherited_fl to TRUE if it's found on upper levels.
@param cond_equal multiple equalities to search in
@param item_field field to look for
@param[out] inherited_fl set up to TRUE if multiple equality is found
on upper levels (not on current level of
cond_equal)
@return
- Item_equal for the found multiple equality predicate if a success;
- NULL otherwise.
*/
Item_equal *find_item_equal(COND_EQUAL *cond_equal, Item_field *item_field,
bool *inherited_fl)
{
Item_equal *item= 0;
bool in_upper_level= FALSE;
while (cond_equal)
{
List_iterator_fast<Item_equal> li(cond_equal->current_level);
while ((item= li++))
{
if (item->contains(item_field->field))
goto finish;
}
in_upper_level= TRUE;
cond_equal= cond_equal->upper_levels;
}
in_upper_level= FALSE;
finish:
*inherited_fl= in_upper_level;
return item;
}
/**
Get the best field substitution for a given field.
If the field is member of a multiple equality, look up that equality
and return the most appropriate field. Usually this is the equivalenced
field belonging to the outer-most table in the join order, but
@see Item_field::get_subst_item() for details.
Otherwise, return the same field.
@param item_field The field that we are seeking a substitution for.
@param cond_equal multiple equalities to search in
@return The substituted field.
*/
Item_field *get_best_field(Item_field *item_field, COND_EQUAL *cond_equal)
{
bool dummy;
Item_equal *item_eq= find_item_equal(cond_equal, item_field, &dummy);
if (!item_eq)
return item_field;
return item_eq->get_subst_item(item_field);
}
/**
Check whether an equality can be used to build multiple equalities.
This function first checks whether the equality (left_item=right_item)
is a simple equality i.e. one that equates a field with another field
or a constant (field=field_item or field=const_item).
If this is the case the function looks for a multiple equality
in the lists referenced directly or indirectly by cond_equal inferring
the given simple equality. If it doesn't find any, it builds a multiple
equality that covers the predicate, i.e. the predicate can be inferred
from this multiple equality.
The built multiple equality could be obtained in such a way:
create a binary multiple equality equivalent to the predicate, then
merge it, if possible, with one of old multiple equalities.
This guarantees that the set of multiple equalities covering equality
predicates will be minimal.
EXAMPLE:
For the where condition
@code
WHERE a=b AND b=c AND
(b=2 OR f=e)
@endcode
the check_equality will be called for the following equality
predicates a=b, b=c, b=2 and f=e.
- For a=b it will be called with *cond_equal=(0,[]) and will transform
*cond_equal into (0,[Item_equal(a,b)]).
- For b=c it will be called with *cond_equal=(0,[Item_equal(a,b)])
and will transform *cond_equal into CE=(0,[Item_equal(a,b,c)]).
- For b=2 it will be called with *cond_equal=(ptr(CE),[])
and will transform *cond_equal into (ptr(CE),[Item_equal(2,a,b,c)]).
- For f=e it will be called with *cond_equal=(ptr(CE), [])
and will transform *cond_equal into (ptr(CE),[Item_equal(f,e)]).
@note
Now only fields that have the same type definitions (verified by
the Field::eq_def method) are placed to the same multiple equalities.
Because of this some equality predicates are not eliminated and
can be used in the constant propagation procedure.
We could weaken the equality test as soon as at least one of the
equal fields is to be equal to a constant. It would require a
more complicated implementation: we would have to store, in
general case, its own constant for each fields from the multiple
equality. But at the same time it would allow us to get rid
of constant propagation completely: it would be done by the call
to build_equal_items_for_cond.
The implementation does not follow exactly the above rules to
build a new multiple equality for the equality predicate.
If it processes the equality of the form field1=field2, it
looks for multiple equalities me1 containing field1 and me2 containing
field2. If only one of them is found the function expands it with
the lacking field. If multiple equalities for both fields are
found they are merged. If both searches fail a new multiple equality
containing just field1 and field2 is added to the existing
multiple equalities.
If the function processes the predicate of the form field1=const,
it looks for a multiple equality containing field1. If found, the
function checks the constant of the multiple equality. If the value
is unknown, it is setup to const. Otherwise the value is compared with
const and the evaluation of the equality predicate is performed.
When expanding/merging equality predicates from the upper levels
the function first copies them for the current level. It looks
acceptable, as this happens rarely. The implementation without
copying would be much more complicated.
@param thd Thread handler
@param left_item left term of the equality to be checked
@param right_item right term of the equality to be checked
@param item equality item if the equality originates from a condition
predicate, 0 if the equality is the result of row
elimination
@param cond_equal multiple equalities that must hold together with the
equality
@param[out] simple_equality
true if the predicate is a simple equality predicate
to be used for building multiple equalities
false otherwise
@returns false if success, true if error
*/
static bool check_simple_equality(THD *thd,
Item *left_item, Item *right_item,
Item *item, COND_EQUAL *cond_equal,
bool *simple_equality)
{
*simple_equality= false;
if (left_item->type() == Item::REF_ITEM &&
down_cast<Item_ref *>(left_item)->ref_type() == Item_ref::VIEW_REF)
{
if (down_cast<Item_ref *>(left_item)->depended_from)
return false;
left_item= left_item->real_item();
}
if (right_item->type() == Item::REF_ITEM &&
down_cast<Item_ref *>(right_item)->ref_type() == Item_ref::VIEW_REF)
{
if (down_cast<Item_ref *>(right_item)->depended_from)
return false;
right_item= right_item->real_item();
}
Item_field *left_item_field, *right_item_field;
if (left_item->type() == Item::FIELD_ITEM &&
right_item->type() == Item::FIELD_ITEM &&
(left_item_field= down_cast<Item_field *>(left_item)) &&
(right_item_field= down_cast<Item_field *>(right_item)) &&
!left_item_field->depended_from &&
!right_item_field->depended_from)
{
/* The predicate the form field1=field2 is processed */
Field *const left_field= left_item_field->field;
Field *const right_field= right_item_field->field;
if (!left_field->eq_def(right_field))
return false;
/* Search for multiple equalities containing field1 and/or field2 */
bool left_copyfl, right_copyfl;
Item_equal *left_item_equal=
find_item_equal(cond_equal, left_item_field, &left_copyfl);
Item_equal *right_item_equal=
find_item_equal(cond_equal, right_item_field, &right_copyfl);
/* As (NULL=NULL) != TRUE we can't just remove the predicate f=f */
if (left_field->eq(right_field)) /* f = f */
{
*simple_equality= !(left_field->maybe_null() && !left_item_equal);
return false;
}
if (left_item_equal && left_item_equal == right_item_equal)
{
/*
The equality predicate is inference of one of the existing
multiple equalities, i.e the condition is already covered
by upper level equalities
*/
*simple_equality= true;
return false;
}
/* Copy the found multiple equalities at the current level if needed */
if (left_copyfl)
{
/* left_item_equal of an upper level contains left_item */
left_item_equal= new Item_equal(left_item_equal);
if (left_item_equal == NULL)
return true;
cond_equal->current_level.push_back(left_item_equal);
}
if (right_copyfl)
{
/* right_item_equal of an upper level contains right_item */
right_item_equal= new Item_equal(right_item_equal);
if (right_item_equal == NULL)
return true;
cond_equal->current_level.push_back(right_item_equal);
}
if (left_item_equal)
{
/* left item was found in the current or one of the upper levels */
if (! right_item_equal)
left_item_equal->add(down_cast<Item_field *>(right_item));
else
{
/* Merge two multiple equalities forming a new one */
if (left_item_equal->merge(thd, right_item_equal))
return true;
/* Remove the merged multiple equality from the list */
List_iterator<Item_equal> li(cond_equal->current_level);
while ((li++) != right_item_equal) ;
li.remove();
}
}
else
{
/* left item was not found neither the current nor in upper levels */
if (right_item_equal)
{
right_item_equal->add(down_cast<Item_field *>(left_item));
}
else
{
/* None of the fields was found in multiple equalities */
Item_equal *item_equal=
new Item_equal(down_cast<Item_field *>(left_item),
down_cast<Item_field *>(right_item));
if (item_equal == NULL)
return true;
cond_equal->current_level.push_back(item_equal);
}
}
*simple_equality= true;
return false;
}
{
/* The predicate of the form field=const/const=field is processed */
Item *const_item= 0;
Item_field *field_item= 0;
if (left_item->type() == Item::FIELD_ITEM &&
(field_item= down_cast<Item_field *>(left_item)) &&
field_item->depended_from == NULL &&
right_item->const_item())
{
const_item= right_item;
}
else if (right_item->type() == Item::FIELD_ITEM &&
(field_item= down_cast<Item_field *>(right_item)) &&
field_item->depended_from == NULL &&
left_item->const_item())
{
const_item= left_item;
}
if (const_item &&
field_item->result_type() == const_item->result_type())
{
if (field_item->result_type() == STRING_RESULT)
{
const CHARSET_INFO *cs= field_item->field->charset();
if (!item)
{
Item_func_eq *const eq_item= new Item_func_eq(left_item, right_item);
if (eq_item == NULL || eq_item->set_cmp_func())
return true;
eq_item->quick_fix_field();
item= eq_item;
}
if ((cs != down_cast<Item_func *>(item)->compare_collation()) ||
!cs->coll->propagate(cs, 0, 0))
return false;
}
bool copyfl;
Item_equal *item_equal= find_item_equal(cond_equal, field_item, ©fl);
if (copyfl)
{
item_equal= new Item_equal(item_equal);
if (item_equal == NULL)
return true;
cond_equal->current_level.push_back(item_equal);
}
if (item_equal)
{
/*
The flag cond_false will be set to 1 after this, if item_equal
already contains a constant and its value is not equal to
the value of const_item.
*/
if (item_equal->add(thd, const_item, field_item))
return true;
}
else
{
item_equal= new Item_equal(const_item, field_item);
if (item_equal == NULL)
return true;
cond_equal->current_level.push_back(item_equal);
}
*simple_equality= true;
return false;
}
}
return false;
}
/**
Convert row equalities into a conjunction of regular equalities.
The function converts a row equality of the form (E1,...,En)=(E'1,...,E'n)
into a list of equalities E1=E'1,...,En=E'n. For each of these equalities
Ei=E'i the function checks whether it is a simple equality or a row
equality. If it is a simple equality it is used to expand multiple
equalities of cond_equal. If it is a row equality it converted to a
sequence of equalities between row elements. If Ei=E'i is neither a
simple equality nor a row equality the item for this predicate is added
to eq_list.
@param thd thread handle
@param left_row left term of the row equality to be processed
@param right_row right term of the row equality to be processed
@param cond_equal multiple equalities that must hold together with the
predicate
@param eq_list results of conversions of row equalities that are not
simple enough to form multiple equalities
@param[out] simple_equality
true if the row equality is composed of only
simple equalities.
@returns false if conversion succeeded, true if any error.
*/
static bool check_row_equality(THD *thd, Item *left_row, Item_row *right_row,
COND_EQUAL *cond_equal, List<Item>* eq_list,
bool *simple_equality)
{
*simple_equality= false;
uint n= left_row->cols();
for (uint i= 0 ; i < n; i++)
{
bool is_converted;
Item *left_item= left_row->element_index(i);
Item *right_item= right_row->element_index(i);
if (left_item->type() == Item::ROW_ITEM &&
right_item->type() == Item::ROW_ITEM)
{
if (check_row_equality(thd,
down_cast<Item_row *>(left_item),
down_cast<Item_row *>(right_item),
cond_equal, eq_list, &is_converted))
return true;
if (!is_converted)
thd->lex->current_select()->cond_count++;
}
else
{
if (check_simple_equality(thd, left_item, right_item, 0, cond_equal,
&is_converted))
return true;
thd->lex->current_select()->cond_count++;
}
if (!is_converted)
{
Item_func_eq *const eq_item= new Item_func_eq(left_item, right_item);
if (eq_item == NULL)
return true;
if (eq_item->set_cmp_func())
{
// Failed to create cmp func -> not only simple equalitities
return true;
}
eq_item->quick_fix_field();
eq_list->push_back(eq_item);
}
}
*simple_equality= true;
return false;
}
/**
Eliminate row equalities and form multiple equalities predicates.
This function checks whether the item is a simple equality
i.e. the one that equates a field with another field or a constant
(field=field_item or field=constant_item), or, a row equality.
For a simple equality the function looks for a multiple equality
in the lists referenced directly or indirectly by cond_equal inferring
the given simple equality. If it doesn't find any, it builds/expands
multiple equality that covers the predicate.
Row equalities are eliminated substituted for conjunctive regular
equalities which are treated in the same way as original equality
predicates.
@param thd thread handle
@param item predicate to process
@param cond_equal multiple equalities that must hold together with the
predicate
@param eq_list results of conversions of row equalities that are not
simple enough to form multiple equalities
@param[out] equality
true if re-writing rules have been applied
false otherwise, i.e.
if the predicate is not an equality, or
if the equality is neither a simple nor a row equality
@returns false if success, true if error
@note If the equality was created by IN->EXISTS, it may be removed later by
subquery materialization. So we don't mix this possibly temporary equality
with others; if we let it go into a multiple-equality (Item_equal), then we
could not remove it later. There is however an exception: if the outer
expression is a constant, it is safe to leave the equality even in
materialization; all it can do is preventing NULL/FALSE distinction but if
such distinction mattered the equality would be in a triggered condition so
we would not come to this function. And injecting constants is good because
it makes the materialized table smaller.
*/
static bool check_equality(THD *thd, Item *item, COND_EQUAL *cond_equal,
List<Item> *eq_list, bool *equality)
{
*equality= false;
Item_func *item_func;
if (item->type() == Item::FUNC_ITEM &&
(item_func= down_cast<Item_func *>(item))->functype() ==
Item_func::EQ_FUNC)
{
Item *left_item= item_func->arguments()[0];
Item *right_item= item_func->arguments()[1];
if (item->created_by_in2exists() && !left_item->const_item())
return false; // See note above
if (left_item->type() == Item::ROW_ITEM &&
right_item->type() == Item::ROW_ITEM)
{
thd->lex->current_select()->cond_count--;
return check_row_equality(thd,
down_cast<Item_row *>(left_item),
down_cast<Item_row *>(right_item),
cond_equal, eq_list, equality);
}
else
return check_simple_equality(thd, left_item, right_item, item, cond_equal,
equality);
}
return false;
}
/**
Replace all equality predicates in a condition by multiple equality items.
At each 'and' level the function detects items for equality predicates
and replaces them by a set of multiple equality items of class Item_equal,
taking into account inherited equalities from upper levels.
If an equality predicate is used not in a conjunction it's just
replaced by a multiple equality predicate.
For each 'and' level the function set a pointer to the inherited
multiple equalities in the cond_equal field of the associated
object of the type Item_cond_and.
The function also traverses the cond tree and for each field reference
sets a pointer to the multiple equality item containing the field, if there
is any. If this multiple equality equates fields to a constant the
function replaces the field reference by the constant in the cases
when the field is not of a string type or when the field reference is
just an argument of a comparison predicate.
The function also determines the maximum number of members in
equality lists of each Item_cond_and object assigning it to
thd->lex->current_select()->max_equal_elems.
@note
Multiple equality predicate =(f1,..fn) is equivalent to the conjuction of
f1=f2, .., fn-1=fn. It substitutes any inference from these
equality predicates that is equivalent to the conjunction.
Thus, =(a1,a2,a3) can substitute for ((a1=a3) AND (a2=a3) AND (a2=a1)) as
it is equivalent to ((a1=a2) AND (a2=a3)).
The function always makes a substitution of all equality predicates occured
in a conjunction for a minimal set of multiple equality predicates.
This set can be considered as a canonical representation of the
sub-conjunction of the equality predicates.
E.g. (t1.a=t2.b AND t2.b>5 AND t1.a=t3.c) is replaced by
(=(t1.a,t2.b,t3.c) AND t2.b>5), not by
(=(t1.a,t2.b) AND =(t1.a,t3.c) AND t2.b>5);
while (t1.a=t2.b AND t2.b>5 AND t3.c=t4.d) is replaced by
(=(t1.a,t2.b) AND =(t3.c=t4.d) AND t2.b>5),
but if additionally =(t4.d,t2.b) is inherited, it
will be replaced by (=(t1.a,t2.b,t3.c,t4.d) AND t2.b>5)
The function performs the substitution in a recursive descent of
the condition tree, passing to the next AND level a chain of multiple
equality predicates which have been built at the upper levels.
The Item_equal items built at the level are attached to other
non-equality conjuncts as a sublist. The pointer to the inherited
multiple equalities is saved in the and condition object (Item_cond_and).
This chain allows us for any field reference occurence to easily find a
multiple equality that must be held for this occurence.
For each AND level we do the following:
- scan it for all equality predicate (=) items
- join them into disjoint Item_equal() groups
- process the included OR conditions recursively to do the same for
lower AND levels.
We need to do things in this order as lower AND levels need to know about
all possible Item_equal objects in upper levels.
@param thd thread handle
@param cond condition(expression) where to make replacement
@param[out] retcond returned condition
@param inherited path to all inherited multiple equality items
@param do_inherit whether or not to inherit equalities from other parts
of the condition
@returns false if success, true if error
*/
static bool build_equal_items_for_cond(THD *thd, Item *cond, Item **retcond,
COND_EQUAL *inherited, bool do_inherit)
{
Item_equal *item_equal;
COND_EQUAL cond_equal;
cond_equal.upper_levels= inherited;
if (check_stack_overrun(thd, STACK_MIN_SIZE, NULL))
return true; // Fatal error flag is set!
const enum Item::Type cond_type= cond->type();
if (cond_type == Item::COND_ITEM)
{
List<Item> eq_list;
Item_cond *const item_cond= down_cast<Item_cond *>(cond);
const bool and_level= item_cond->functype() == Item_func::COND_AND_FUNC;
List<Item> *args= item_cond->argument_list();
List_iterator<Item> li(*args);
Item *item;
if (and_level)
{
/*
Retrieve all conjuncts of this level detecting the equality
that are subject to substitution by multiple equality items and
removing each such predicate from the conjunction after having
found/created a multiple equality whose inference the predicate is.
*/
while ((item= li++))
{
/*
PS/SP note: we can safely remove a node from AND-OR
structure here because it's restored before each
re-execution of any prepared statement/stored procedure.
*/
bool equality;
if (check_equality(thd, item, &cond_equal, &eq_list, &equality))
return true;
if (equality)
li.remove();
}
/*
Check if we eliminated all the predicates of the level, e.g.
(a=a AND b=b AND a=a).
*/
if (!args->elements &&
!cond_equal.current_level.elements &&
!eq_list.elements)
{
*retcond= new Item_int((longlong) 1, 1);
return *retcond == NULL;
}
List_iterator_fast<Item_equal> it(cond_equal.current_level);
while ((item_equal= it++))
{
item_equal->fix_length_and_dec();
item_equal->update_used_tables();
set_if_bigger(thd->lex->current_select()->max_equal_elems,
item_equal->members());
}
Item_cond_and *const item_cond_and= down_cast<Item_cond_and *>(cond);
item_cond_and->cond_equal= cond_equal;
inherited= &item_cond_and->cond_equal;
}
/*
Make replacement of equality predicates for lower levels
of the condition expression.
*/
li.rewind();
while ((item= li++))
{
Item *new_item;
if (build_equal_items_for_cond(thd, item, &new_item, inherited,
do_inherit))
return true;
if (new_item != item)
{
/* This replacement happens only for standalone equalities */
/*
This is ok with PS/SP as the replacement is done for
arguments of an AND/OR item, which are restored for each
execution of PS/SP.
*/
li.replace(new_item);
}
}
if (and_level)
{
args->concat(&eq_list);
args->concat((List<Item> *)&cond_equal.current_level);
}
}
else if (cond->type() == Item::FUNC_ITEM)
{
List<Item> eq_list;
/*
If an equality predicate forms the whole and level,
we call it standalone equality and it's processed here.
E.g. in the following where condition
WHERE a=5 AND (b=5 or a=c)
(b=5) and (a=c) are standalone equalities.
In general we can't leave alone standalone eqalities:
for WHERE a=b AND c=d AND (b=c OR d=5)
b=c is replaced by =(a,b,c,d).
*/
bool equality;
if (check_equality(thd, cond, &cond_equal, &eq_list, &equality))
return true;
if (equality)
{
int n= cond_equal.current_level.elements + eq_list.elements;
if (n == 0)
{
*retcond= new Item_int((longlong) 1,1);
return *retcond == NULL;
}
else if (n == 1)
{
if ((item_equal= cond_equal.current_level.pop()))
{
item_equal->fix_length_and_dec();
item_equal->update_used_tables();
set_if_bigger(thd->lex->current_select()->max_equal_elems,
item_equal->members());
*retcond= item_equal;
return false;
}
*retcond= eq_list.pop();
return false;
}
else
{
/*
Here a new AND level must be created. It can happen only
when a row equality is processed as a standalone predicate.
*/
Item_cond_and *and_cond= new Item_cond_and(eq_list);
if (and_cond == NULL)
return true;
and_cond->quick_fix_field();
List<Item> *args= and_cond->argument_list();
List_iterator_fast<Item_equal> it(cond_equal.current_level);
while ((item_equal= it++))
{
item_equal->fix_length_and_dec();
item_equal->update_used_tables();
set_if_bigger(thd->lex->current_select()->max_equal_elems,
item_equal->members());
}
and_cond->cond_equal= cond_equal;
args->concat((List<Item> *)&cond_equal.current_level);
*retcond= and_cond;
return false;
}
}
if (do_inherit)
{
/*
For each field reference in cond, not from equal item predicates,
set a pointer to the multiple equality it belongs to (if there is any)
as soon the field is not of a string type or the field reference is
an argument of a comparison predicate.
*/
uchar *is_subst_valid= (uchar *) 1;
cond= cond->compile(&Item::subst_argument_checker,
&is_subst_valid,
&Item::equal_fields_propagator,
(uchar *) inherited);
if (cond == NULL)
return true;
}
cond->update_used_tables();
}
*retcond= cond;
return false;
}
/**
Build multiple equalities for a WHERE condition and all join conditions that
inherit these multiple equalities.
The function first applies the build_equal_items_for_cond function
to build all multiple equalities for condition cond utilizing equalities
referred through the parameter inherited. The extended set of
equalities is returned in the structure referred by the cond_equal_ref
parameter. After this the function calls itself recursively for
all join conditions whose direct references can be found in join_list
and who inherit directly the multiple equalities just having built.
@note
The join condition used in an outer join operation inherits all equalities
from the join condition of the embedding join, if there is any, or
otherwise - from the where condition.
This fact is not obvious, but presumably can be proved.
Consider the following query:
@code
SELECT * FROM (t1,t2) LEFT JOIN (t3,t4) ON t1.a=t3.a AND t2.a=t4.a
WHERE t1.a=t2.a;
@endcode
If the join condition in the query inherits =(t1.a,t2.a), then we
can build the multiple equality =(t1.a,t2.a,t3.a,t4.a) that infers
the equality t3.a=t4.a. Although the join condition
t1.a=t3.a AND t2.a=t4.a AND t3.a=t4.a is not equivalent to the one
in the query the latter can be replaced by the former: the new query
will return the same result set as the original one.
Interesting that multiple equality =(t1.a,t2.a,t3.a,t4.a) allows us
to use t1.a=t3.a AND t3.a=t4.a under the join condition:
@code
SELECT * FROM (t1,t2) LEFT JOIN (t3,t4) ON t1.a=t3.a AND t3.a=t4.a
WHERE t1.a=t2.a
@endcode
This query equivalent to:
@code
SELECT * FROM (t1 LEFT JOIN (t3,t4) ON t1.a=t3.a AND t3.a=t4.a),t2
WHERE t1.a=t2.a
@endcode
Similarly the original query can be rewritten to the query:
@code
SELECT * FROM (t1,t2) LEFT JOIN (t3,t4) ON t2.a=t4.a AND t3.a=t4.a
WHERE t1.a=t2.a
@endcode
that is equivalent to:
@code
SELECT * FROM (t2 LEFT JOIN (t3,t4)ON t2.a=t4.a AND t3.a=t4.a), t1
WHERE t1.a=t2.a
@endcode
Thus, applying equalities from the where condition we basically
can get more freedom in performing join operations.
Although we don't use this property now, it probably makes sense to use
it in the future.
@param thd Thread handler
@param cond condition to build the multiple equalities for
@param[out] retcond Returned condition
@param inherited path to all inherited multiple equality items
@param do_inherit whether or not to inherit equalities from other
parts of the condition
@param join_list list of join tables that the condition refers to
@param[out] cond_equal_ref pointer to the structure to place built
equalities in
@returns false if success, true if error
*/
bool build_equal_items(THD *thd, Item *cond, Item **retcond,
COND_EQUAL *inherited, bool do_inherit,
List<TABLE_LIST> *join_list,
COND_EQUAL **cond_equal_ref)
{
COND_EQUAL *cond_equal= 0;
if (cond)
{
if (build_equal_items_for_cond(thd, cond, &cond, inherited, do_inherit))
return true;
cond->update_used_tables();
const enum Item::Type cond_type= cond->type();
if (cond_type == Item::COND_ITEM &&
down_cast<Item_cond *>(cond)->functype() == Item_func::COND_AND_FUNC)
cond_equal= &down_cast<Item_cond_and *>(cond)->cond_equal;
else if (cond_type == Item::FUNC_ITEM &&
down_cast<Item_func *>(cond)->functype() == Item_func::MULT_EQUAL_FUNC)
{
cond_equal= new COND_EQUAL;
if (cond_equal == NULL)
return true;
cond_equal->current_level.push_back(down_cast<Item_equal *>(cond));
}
}
if (cond_equal)
{
cond_equal->upper_levels= inherited;
inherited= cond_equal;
}
*cond_equal_ref= cond_equal;
if (join_list)
{
TABLE_LIST *table;
List_iterator<TABLE_LIST> li(*join_list);
while ((table= li++))
{
if (table->join_cond_optim())
{
List<TABLE_LIST> *nested_join_list= table->nested_join ?
&table->nested_join->join_list : NULL;
Item *join_cond;
if (build_equal_items(thd, table->join_cond_optim(), &join_cond,
inherited, do_inherit,
nested_join_list, &table->cond_equal))
return true;
table->set_join_cond_optim(join_cond);
}
}
}
*retcond= cond;
return false;
}
/**
Compare field items by table order in the execution plan.
field1 considered as better than field2 if the table containing
field1 is accessed earlier than the table containing field2.
The function finds out what of two fields is better according
this criteria.
@param field1 first field item to compare
@param field2 second field item to compare
@param table_join_idx index to tables determining table order
@retval
-1 if field1 is better than field2
@retval
1 if field2 is better than field1
@retval
0 otherwise
*/
static int compare_fields_by_table_order(Item_field *field1,
Item_field *field2,
void *table_join_idx)
{
int cmp= 0;
bool outer_ref= 0;
if (field1->used_tables() & OUTER_REF_TABLE_BIT)
{
outer_ref= 1;
cmp= -1;
}
if (field2->used_tables() & OUTER_REF_TABLE_BIT)
{
outer_ref= 1;
cmp++;
}
if (outer_ref)
return cmp;
JOIN_TAB **idx= (JOIN_TAB **) table_join_idx;
/*
idx is NULL if this function was not called from JOIN::optimize()
but from e.g. mysql_delete() or mysql_update(). In these cases
there is only one table and both fields belong to it. Example
condition where this is the case: t1.fld1=t1.fld2
*/
if (!idx)
return 0;
// Locate JOIN_TABs thanks to table_join_idx, then compare their index.
cmp= idx[field1->table_ref->tableno()]->idx() -
idx[field2->table_ref->tableno()]->idx();
return cmp < 0 ? -1 : (cmp ? 1 : 0);
}
/**
Generate minimal set of simple equalities equivalent to a multiple equality.
The function retrieves the fields of the multiple equality item
item_equal and for each field f:
- if item_equal contains const it generates the equality f=const_item;
- otherwise, if f is not the first field, generates the equality
f=item_equal->get_first().
All generated equality are added to the cond conjunction.
@param cond condition to add the generated equality to
@param upper_levels structure to access multiple equality of upper levels
@param item_equal multiple equality to generate simple equality from
@note
Before generating an equality function checks that it has not
been generated for multiple equalities of the upper levels.
E.g. for the following where condition
WHERE a=5 AND ((a=b AND b=c) OR c>4)
the upper level AND condition will contain =(5,a),
while the lower level AND condition will contain =(5,a,b,c).
When splitting =(5,a,b,c) into a separate equality predicates
we should omit 5=a, as we have it already in the upper level.
The following where condition gives us a more complicated case:
WHERE t1.a=t2.b AND t3.c=t4.d AND (t2.b=t3.c OR t4.e>5 ...) AND ...
Given the tables are accessed in the order t1->t2->t3->t4 for
the selected query execution plan the lower level multiple
equality =(t1.a,t2.b,t3.c,t4.d) formally should be converted to
t1.a=t2.b AND t1.a=t3.c AND t1.a=t4.d. But t1.a=t2.a will be
generated for the upper level. Also t3.c=t4.d will be generated there.
So only t1.a=t3.c should be left in the lower level.
If cond is equal to 0, then not more then one equality is generated
and a pointer to it is returned as the result of the function.
@return
- The condition with generated simple equalities or
a pointer to the simple generated equality, if success.
- 0, otherwise.
*/
static Item *eliminate_item_equal(Item *cond, COND_EQUAL *upper_levels,
Item_equal *item_equal)
{
List<Item> eq_list;
Item_func_eq *eq_item= NULL;
if (((Item *) item_equal)->const_item() && !item_equal->val_int())
return new Item_int((longlong) 0,1);
Item *const item_const= item_equal->get_const();
Item_equal_iterator it(*item_equal);
if (!item_const)
{
/*
If there is a const item, match all field items with the const item,
otherwise match the second and subsequent field items with the first one:
*/
it++;
}
Item_field *item_field; // Field to generate equality for.
while ((item_field= it++))
{
/*
Generate an equality of the form:
item_field = some previous field in item_equal's list.
First see if we really need to generate it:
*/
Item_equal *const upper= item_field->find_item_equal(upper_levels);
if (upper) // item_field is in this upper equality
{
if (item_const && upper->get_const())
continue; // Const at both levels, no need to generate at current level
/*
If the upper-level multiple equality contains this item, there is no
need to generate the equality, unless item_field belongs to a
semi-join nest that is used for Materialization, and refers to tables
that are outside of the materialized semi-join nest,
As noted in Item_equal::get_subst_item(), subquery materialization
does not have this problem.
*/
JOIN_TAB *const tab= item_field->field->table->reginfo.join_tab;
if (!(tab && sj_is_materialize_strategy(tab->get_sj_strategy())))
{
Item_field *item_match;
Item_equal_iterator li(*item_equal);
while ((item_match= li++) != item_field)
{
if (item_match->find_item_equal(upper_levels) == upper)
break; // (item_match, item_field) is also in upper level equality
}
if (item_match != item_field)
continue;
}
} // ... if (upper).
/*
item_field should be compared with the head of the multiple equality
list.
item_field may refer to a table that is within a semijoin materialization
nest. In that case, the order of the join_tab entries may look like:
ot1 ot2 <subquery> ot5 SJM(it3 it4)
If we have a multiple equality
(ot1.c1, ot2.c2, <subquery>.c it3.c3, it4.c4, ot5.c5),
we should generate the following equalities:
1. ot1.c1 = ot2.c2
2. ot1.c1 = <subquery>.c
3. it3.c3 = it4.c4
4. ot1.c1 = ot5.c5
Equalities 1) and 4) are regular equalities between two outer tables.
Equality 2) is an equality that matches the outer query with a
materialized temporary table. It is either performed as a lookup
into the materialized table (SJM-lookup), or as a condition on the
outer table (SJM-scan).
Equality 3) is evaluated during semijoin materialization.
If there is a const item, match against this one.
Otherwise, match against the first field item in the multiple equality,
unless the item is within a materialized semijoin nest, in case it will
be matched against the first item within the SJM nest.
@see JOIN::set_prefix_tables()
@see Item_equal::get_subst_item()
*/
Item *const head=
item_const ? item_const : item_equal->get_subst_item(item_field);
if (head == item_field)
continue;
// we have a pair, can generate 'item_field=head'
if (eq_item)
eq_list.push_back(eq_item);
eq_item= new Item_func_eq(item_field, head);
if (!eq_item || eq_item->set_cmp_func())
return NULL;
eq_item->quick_fix_field();
} // ... while ((item_field= it++))
if (!cond && !eq_list.head())
{
if (!eq_item)
return new Item_int((longlong) 1,1);
return eq_item;
}
if (eq_item)
eq_list.push_back(eq_item);
if (!cond)
cond= new Item_cond_and(eq_list);
else
{
assert(cond->type() == Item::COND_ITEM);
if (eq_list.elements)
((Item_cond *) cond)->add_at_head(&eq_list);
}
cond->quick_fix_field();
cond->update_used_tables();
return cond;
}
/**
Substitute every field reference in a condition by the best equal field
and eliminate all multiple equality predicates.
The function retrieves the cond condition and for each encountered
multiple equality predicate it sorts the field references in it
according to the order of tables specified by the table_join_idx
parameter. Then it eliminates the multiple equality predicate it
replacing it by the conjunction of simple equality predicates
equating every field from the multiple equality to the first
field in it, or to the constant, if there is any.
After this the function retrieves all other conjuncted
predicates substitute every field reference by the field reference
to the first equal field or equal constant if there are any.
@param cond condition to process
@param cond_equal multiple equalities to take into consideration
@param table_join_idx index to tables determining field preference
@note
At the first glance full sort of fields in multiple equality
seems to be an overkill. Yet it's not the case due to possible
new fields in multiple equality item of lower levels. We want
the order in them to comply with the order of upper levels.
@return
The transformed condition, or NULL in case of error
*/
Item* substitute_for_best_equal_field(Item *cond,
COND_EQUAL *cond_equal,
void *table_join_idx)
{
Item_equal *item_equal;
if (cond->type() == Item::COND_ITEM)
{
List<Item> *cond_list= ((Item_cond*) cond)->argument_list();
bool and_level= ((Item_cond*) cond)->functype() ==
Item_func::COND_AND_FUNC;
if (and_level)
{
cond_equal= &((Item_cond_and *) cond)->cond_equal;
cond_list->disjoin((List<Item> *) &cond_equal->current_level);
List_iterator_fast<Item_equal> it(cond_equal->current_level);
while ((item_equal= it++))
{
item_equal->sort(&compare_fields_by_table_order, table_join_idx);
}
}
List_iterator<Item> li(*cond_list);
Item *item;
while ((item= li++))
{
Item *new_item= substitute_for_best_equal_field(item, cond_equal,
table_join_idx);
if (new_item == NULL)
return NULL;
/*
This works OK with PS/SP re-execution as changes are made to
the arguments of AND/OR items only
*/
if (new_item != item)
li.replace(new_item);
}
if (and_level)
{
List_iterator_fast<Item_equal> it(cond_equal->current_level);
while ((item_equal= it++))
{
cond= eliminate_item_equal(cond, cond_equal->upper_levels, item_equal);
if (cond == NULL)
return NULL;
// This occurs when eliminate_item_equal() founds that cond is
// always false and substitutes it with Item_int 0.
// Due to this, value of item_equal will be 0, so just return it.
if (cond->type() != Item::COND_ITEM)
break;
}
}
if (cond->type() == Item::COND_ITEM &&
!((Item_cond*)cond)->argument_list()->elements)
cond= new Item_int((int32)cond->val_bool());
}
else if (cond->type() == Item::FUNC_ITEM &&
((Item_cond*) cond)->functype() == Item_func::MULT_EQUAL_FUNC)
{
item_equal= (Item_equal *) cond;
item_equal->sort(&compare_fields_by_table_order, table_join_idx);
if (cond_equal && cond_equal->current_level.head() == item_equal)
cond_equal= cond_equal->upper_levels;
return eliminate_item_equal(0, cond_equal, item_equal);
}
else
cond->transform(&Item::replace_equal_field, 0);
return cond;
}
/**
change field = field to field = const for each found field = const in the
and_level
@param thd Thread handler
@param save_list
@param and_father
@param cond Condition where fields are replaced with constant values
@param field The field that will be substituted
@param value The substitution value
@returns false if success, true if error
*/
static bool
change_cond_ref_to_const(THD *thd, I_List<COND_CMP> *save_list,
Item *and_father, Item *cond,
Item *field, Item *value)
{
if (cond->type() == Item::COND_ITEM)
{
Item_cond *const item_cond= down_cast<Item_cond *>(cond);
bool and_level= item_cond->functype() == Item_func::COND_AND_FUNC;
List_iterator<Item> li(*item_cond->argument_list());
Item *item;
while ((item=li++))
{
if (change_cond_ref_to_const(thd, save_list,
and_level ? cond : item,
item, field, value))
return true;
}
return false;
}
if (cond->eq_cmp_result() == Item::COND_OK)
return false; // Not a boolean function
Item_bool_func2 *func= down_cast<Item_bool_func2 *>(cond);
Item **args= func->arguments();
Item *left_item= args[0];
Item *right_item= args[1];
Item_func::Functype functype= func->functype();
if (right_item->eq(field,0) && left_item != value &&
right_item->cmp_context == field->cmp_context &&
(left_item->result_type() != STRING_RESULT ||
value->result_type() != STRING_RESULT ||
left_item->collation.collation == value->collation.collation))
{
Item *const clone= value->clone_item();
if (thd->is_error())
return true;
if (clone == NULL)
return false;
clone->collation.set(right_item->collation);
thd->change_item_tree(args + 1, clone);
func->update_used_tables();
if ((functype == Item_func::EQ_FUNC ||
functype == Item_func::EQUAL_FUNC) &&
and_father != cond && !left_item->const_item())
{
cond->marker=1;
COND_CMP *const cond_cmp= new COND_CMP(and_father,func);
if (cond_cmp == NULL)
return true;
save_list->push_back(cond_cmp);
}
if (func->set_cmp_func())
return true;
}
else if (left_item->eq(field,0) && right_item != value &&
left_item->cmp_context == field->cmp_context &&
(right_item->result_type() != STRING_RESULT ||
value->result_type() != STRING_RESULT ||
right_item->collation.collation == value->collation.collation))
{
Item *const clone= value->clone_item();
if (thd->is_error())
return true;
if (clone == NULL)
return false;
clone->collation.set(left_item->collation);
thd->change_item_tree(args, clone);
value= clone;
func->update_used_tables();
if ((functype == Item_func::EQ_FUNC ||
functype == Item_func::EQUAL_FUNC) &&
and_father != cond && !right_item->const_item())
{
args[0]= args[1]; // For easy check
thd->change_item_tree(args + 1, value);
cond->marker=1;
COND_CMP *const cond_cmp= new COND_CMP(and_father,func);
if (cond_cmp == NULL)
return true;
save_list->push_back(cond_cmp);
}
if (func->set_cmp_func())
return true;
}
return false;
}
/**
Propagate constant values in a condition
@param thd Thread handler
@param save_list
@param and_father
@param cond Condition for which constant values are propagated
@returns false if success, true if error
*/
static bool
propagate_cond_constants(THD *thd, I_List<COND_CMP> *save_list,
Item *and_father, Item *cond)
{
if (cond->type() == Item::COND_ITEM)
{
Item_cond *const item_cond= down_cast<Item_cond *>(cond);
bool and_level= item_cond->functype() == Item_func::COND_AND_FUNC;
List_iterator_fast<Item> li(*item_cond->argument_list());
Item *item;
I_List<COND_CMP> save;
while ((item=li++))
{
if (propagate_cond_constants(thd, &save, and_level ? cond : item, item))
return true;
}
if (and_level)
{ // Handle other found items
I_List_iterator<COND_CMP> cond_itr(save);
COND_CMP *cond_cmp;
while ((cond_cmp= cond_itr++))
{
Item **args= cond_cmp->cmp_func->arguments();
if (!args[0]->const_item() &&
change_cond_ref_to_const(thd, &save, cond_cmp->and_level,
cond_cmp->and_level, args[0], args[1]))
return true;
}
}
}
else if (and_father != cond && !cond->marker) // In a AND group
{
Item_func *func;
if (cond->type() == Item::FUNC_ITEM &&
(func= down_cast<Item_func *>(cond)) &&
(func->functype() == Item_func::EQ_FUNC ||
func->functype() == Item_func::EQUAL_FUNC))
{
Item **args= func->arguments();
bool left_const= args[0]->const_item();
bool right_const= args[1]->const_item();
if (!(left_const && right_const) &&
args[0]->result_type() == args[1]->result_type())
{
if (right_const)
{
if (resolve_const_item(thd, &args[1], args[0]))
return true;
func->update_used_tables();
if (change_cond_ref_to_const(thd, save_list, and_father, and_father,
args[0], args[1]))
return true;
}
else if (left_const)
{
if (resolve_const_item(thd, &args[0], args[1]))
return true;
func->update_used_tables();
if (change_cond_ref_to_const(thd, save_list, and_father, and_father,
args[1], args[0]))
return true;
}
}
}
}
return false;
}
/**
Assign each nested join structure a bit in nested_join_map.
@param join_list List of tables
@param first_unused Number of first unused bit in nested_join_map before the
call
@note
This function is called after simplify_joins(), when there are no
redundant nested joins.
We cannot have more nested joins in a query block than there are tables,
so as long as the number of bits in nested_join_map is not less than the
maximum number of tables in a query block, nested_join_map can never
overflow.
@return
First unused bit in nested_join_map after the call.
*/
uint build_bitmap_for_nested_joins(List<TABLE_LIST> *join_list,
uint first_unused)
{
List_iterator<TABLE_LIST> li(*join_list);
TABLE_LIST *table;
DBUG_ENTER("build_bitmap_for_nested_joins");
while ((table= li++))
{
NESTED_JOIN *nested_join;
if ((nested_join= table->nested_join))
{
// We should have either a join condition or a semi-join condition
assert((table->join_cond() == NULL) == (table->sj_cond() != NULL));
nested_join->nj_map= 0;
nested_join->nj_total= 0;
/*
We only record nested join information for outer join nests.
Tables belonging in semi-join nests are recorded in the
embedding outer join nest, if one exists.
*/
if (table->join_cond())
{
assert(first_unused < sizeof(nested_join_map)*8);
nested_join->nj_map= (nested_join_map) 1 << first_unused++;
nested_join->nj_total= nested_join->join_list.elements;
}
else if (table->sj_cond())
{
NESTED_JOIN *const outer_nest=
table->embedding ? table->embedding->nested_join : NULL;
/*
The semi-join nest has already been counted into the table count
for the outer join nest as one table, so subtract 1 from the
table count.
*/
if (outer_nest)
outer_nest->nj_total+= (nested_join->join_list.elements - 1);
}
else
assert(false);
first_unused= build_bitmap_for_nested_joins(&nested_join->join_list,
first_unused);
}
}
DBUG_RETURN(first_unused);
}
/** Update the dependency map for the tables. */
void JOIN::update_depend_map()
{
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
for (uint tableno = 0; tableno < tables; tableno++)
{
JOIN_TAB *const tab= best_ref[tableno];
TABLE_REF *const ref= &tab->ref();
table_map depend_map= 0;
Item **item= ref->items;
for (uint i = 0; i < ref->key_parts; i++, item++)
depend_map|= (*item)->used_tables();
depend_map&= ~PSEUDO_TABLE_BITS;
ref->depend_map= depend_map;
for (JOIN_TAB **tab2= map2table; depend_map; tab2++, depend_map >>= 1)
{
if (depend_map & 1)
ref->depend_map|= (*tab2)->ref().depend_map;
}
}
}
/** Update the dependency map for the sort order. */
void JOIN::update_depend_map(ORDER *order)
{
for (; order ; order=order->next)
{
table_map depend_map;
order->item[0]->update_used_tables();
order->depend_map= depend_map=
order->item[0]->used_tables() & ~PARAM_TABLE_BIT;
order->used= 0;
// Not item_sum(), RAND() and no reference to table outside of sub select
if (!(order->depend_map & (OUTER_REF_TABLE_BIT | RAND_TABLE_BIT))
&& !order->item[0]->with_sum_func)
{
for (JOIN_TAB **tab= map2table; depend_map; tab++, depend_map >>= 1)
{
if (depend_map & 1)
order->depend_map|=(*tab)->ref().depend_map;
}
}
}
}
/**
Update equalities and keyuse references after semi-join materialization
strategy is chosen.
@details
For each multiple equality that contains a field that is selected
from a subquery, and that subquery is executed using a semi-join
materialization strategy, add the corresponding column in the materialized
temporary table to the equality.
For each injected semi-join equality that is not converted to
multiple equality, replace the reference to the expression selected
from the subquery with the corresponding column in the temporary table.
This is needed to properly reflect the equalities that involve injected
semi-join equalities when materialization strategy is chosen.
@see eliminate_item_equal() for how these equalities are used to generate
correct equality predicates.
The MaterializeScan semi-join strategy requires some additional processing:
All primary tables after the materialized temporary table must be inspected
for keyuse objects that point to expressions from the subquery tables.
These references must be replaced with references to corresponding columns
in the materialized temporary table instead. Those primary tables using
ref access will thus be made to depend on the materialized temporary table
instead of the subquery tables.
Only the injected semi-join equalities need this treatment, other predicates
will be handled correctly by the regular item substitution process.
@return False if success, true if error
*/
bool JOIN::update_equalities_for_sjm()
{
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
List_iterator<Semijoin_mat_exec> it(sjm_exec_list);
Semijoin_mat_exec *sjm_exec;
while ((sjm_exec= it++))
{
TABLE_LIST *const sj_nest= sjm_exec->sj_nest;
assert(!sj_nest->outer_join_nest());
/*
A materialized semi-join nest cannot actually be an inner part of an
outer join yet, this is just a preparatory step,
ie sj_nest->outer_join_nest() is always NULL here.
@todo: Enable outer joining here later.
*/
Item *cond= sj_nest->outer_join_nest() ?
sj_nest->outer_join_nest()->join_cond_optim() : where_cond;
if (!cond)
continue;
uchar *dummy= NULL;
cond= cond->compile(&Item::equality_substitution_analyzer, &dummy,
&Item::equality_substitution_transformer,
(uchar *)sj_nest);
if (cond == NULL)
return true;
cond->update_used_tables();
// Loop over all primary tables that follow the materialized table
for (uint j= sjm_exec->mat_table_index + 1; j < primary_tables; j++)
{
JOIN_TAB *const tab= best_ref[j];
for (Key_use *keyuse= tab->position()->key;
keyuse && keyuse->table_ref == tab->table_ref &&
keyuse->key == tab->position()->key->key;
keyuse++)
{
List_iterator<Item> it(sj_nest->nested_join->sj_inner_exprs);
Item *old;
uint fieldno= 0;
while ((old= it++))
{
if (old->real_item()->eq(keyuse->val->real_item(), false))
{
/*
Replace the expression selected from the subquery with the
corresponding column of the materialized temporary table.
*/
keyuse->val= sj_nest->nested_join->sjm.mat_fields[fieldno];
keyuse->used_tables= keyuse->val->used_tables();
break;
}
fieldno++;
}
}
}
}
return false;
}
/**
Assign set of available (prefix) tables to all tables in query block.
Also set added tables, ie the tables added in each JOIN_TAB compared to the
previous JOIN_TAB.
This function must be called for every query block after the table order
has been determined.
*/
void JOIN::set_prefix_tables()
{
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
assert(!plan_is_const());
/*
The const tables are available together with the first non-const table in
the join order.
*/
table_map const initial_tables_map= const_table_map |
(allow_outer_refs ? OUTER_REF_TABLE_BIT : 0);
table_map current_tables_map= initial_tables_map;
table_map prev_tables_map= (table_map) 0;
table_map saved_tables_map= (table_map) 0;
JOIN_TAB *last_non_sjm_tab= NULL; // Track the last non-sjm table
for (uint i= const_tables; i < tables; i++)
{
JOIN_TAB *const tab= best_ref[i];
if (!tab->table())
continue;
/*
Tables that are within SJ-Materialization nests cannot have their
conditions referring to preceding non-const tables.
- If we're looking at the first SJM table, reset current_tables_map
to refer to only allowed tables
@see Item_equal::get_subst_item()
@see eliminate_item_equal()
*/
if (sj_is_materialize_strategy(tab->get_sj_strategy()))
{
const table_map sjm_inner_tables= tab->emb_sj_nest->sj_inner_tables;
if (!(sjm_inner_tables & current_tables_map))
{
saved_tables_map= current_tables_map;
current_tables_map= initial_tables_map;
prev_tables_map= (table_map) 0;
}
current_tables_map|= tab->table_ref->map();
tab->set_prefix_tables(current_tables_map, prev_tables_map);
prev_tables_map= current_tables_map;
if (!(sjm_inner_tables & ~current_tables_map))
{
/*
At the end of a semi-join materialization nest,
add non-deterministic expressions to the last table of the nest:
*/
tab->add_prefix_tables(RAND_TABLE_BIT);
// Restore the previous map:
current_tables_map= saved_tables_map;
prev_tables_map= last_non_sjm_tab ?
last_non_sjm_tab->prefix_tables() : (table_map) 0;
}
}
else
{
last_non_sjm_tab= tab;
current_tables_map|= tab->table_ref->map();
tab->set_prefix_tables(current_tables_map, prev_tables_map);
prev_tables_map= current_tables_map;
}
}
/*
Non-deterministic expressions must be added to the last table's condition.
It solves problem with queries like SELECT * FROM t1 WHERE rand() > 0.5
*/
if (last_non_sjm_tab != NULL)
last_non_sjm_tab->add_prefix_tables(RAND_TABLE_BIT);
}
/**
Calculate best possible join order and initialize the join structure.
@return true if success, false if error.
The JOIN object is populated with statistics about the query,
and a plan with table order and access method selection is made.
The list of tables to be optimized is taken from select_lex->leaf_tables.
JOIN::where_cond is also used in the optimization.
As a side-effect, JOIN::keyuse_array is populated with key_use information.
Here is an overview of the logic of this function:
- Initialize JOIN data structures and setup basic dependencies between tables.
- Update dependencies based on join information.
- Make key descriptions (update_ref_and_keys()).
- Pull out semi-join tables based on table dependencies.
- Extract tables with zero or one rows as const tables.
- Read contents of const tables, substitute columns from these tables with
actual data. Also keep track of empty tables vs. one-row tables.
- After const table extraction based on row count, more tables may
have become functionally dependent. Extract these as const tables.
- Add new sargable predicates based on retrieved const values.
- Calculate number of rows to be retrieved from each table.
- Calculate cost of potential semi-join materializations.
- Calculate best possible join order based on available statistics.
- Fill in remaining information for the generated join order.
*/
bool JOIN::make_join_plan()
{
DBUG_ENTER("JOIN::make_join_plan");
SARGABLE_PARAM *sargables= NULL;
Opt_trace_context * const trace= &thd->opt_trace;
if (init_planner_arrays()) // Create and initialize the arrays
DBUG_RETURN(true);
// Outer join dependencies were initialized above, now complete the analysis.
if (select_lex->outer_join)
propagate_dependencies();
if (unlikely(trace->is_started()))
trace_table_dependencies(trace, join_tab, primary_tables);
// Build the key access information, which is the basis for ref access.
if (where_cond || select_lex->outer_join)
{
if (update_ref_and_keys(thd, &keyuse_array, join_tab, tables, where_cond,
cond_equal, ~select_lex->outer_join, select_lex,
&sargables))
DBUG_RETURN(true);
}
/*
Pull out semi-join tables based on dependencies. Dependencies are valid
throughout the lifetime of a query, so this operation can be performed
on the first optimization only.
*/
if (!select_lex->sj_pullout_done && select_lex->sj_nests.elements &&
pull_out_semijoin_tables(this))
DBUG_RETURN(true);
select_lex->sj_pullout_done= true;
const uint sj_nests= select_lex->sj_nests.elements; // Changed by pull-out
if (!(select_lex->active_options() & OPTION_NO_CONST_TABLES))
{
// Detect tables that are const (0 or 1 row) and read their contents.
if (extract_const_tables())
DBUG_RETURN(true);
// Detect tables that are functionally dependent on const values.
if (extract_func_dependent_tables())
DBUG_RETURN(true);
}
// Possibly able to create more sargable predicates from const rows.
if (const_tables && sargables)
update_sargable_from_const(sargables);
// Make a first estimate of the fanout for each table in the query block.
if (estimate_rowcount())
DBUG_RETURN(true);
if (sj_nests)
{
set_semijoin_embedding();
select_lex->update_semijoin_strategies(thd);
}
if (!plan_is_const())
optimize_keyuse();
allow_outer_refs= true;
if (sj_nests && optimize_semijoin_nests_for_materialization(this))
DBUG_RETURN(true);
// Choose the table order based on analysis done so far.
if (Optimize_table_order(thd, this, NULL).choose_table_order())
DBUG_RETURN(true);
DBUG_EXECUTE_IF("bug13820776_1", thd->killed= THD::KILL_QUERY;);
if (thd->killed || thd->is_error())
DBUG_RETURN(true);
// If this is a subquery, decide between In-to-exists and materialization
if (unit->item && decide_subquery_strategy())
DBUG_RETURN(true);
refine_best_rowcount();
if (!(thd->variables.option_bits & OPTION_BIG_SELECTS) &&
best_read > (double) thd->variables.max_join_size &&
!thd->lex->is_explain())
{ /* purecov: inspected */
my_message(ER_TOO_BIG_SELECT, ER(ER_TOO_BIG_SELECT), MYF(0));
error= -1;
DBUG_RETURN(1);
}
positions= NULL; // But keep best_positions for get_best_combination
/*
Store the cost of this query into a user variable
Don't update m_current_query_cost for statements that are not "flat joins" :
i.e. they have subqueries, unions or call stored procedures.
TODO: calculate a correct cost for a query with subqueries and UNIONs.
*/
if (thd->lex->is_single_level_stmt())
thd->m_current_query_cost= best_read;
// Generate an execution plan from the found optimal join order.
if (get_best_combination())
DBUG_RETURN(true);
// Cleanup after update_ref_and_keys has added keys for derived tables.
if (select_lex->materialized_derived_table_count)
drop_unused_derived_keys();
// No need for this struct after new JOIN_TAB array is set up.
best_positions= NULL;
// Some called function may still set error status unnoticed
if (thd->is_error())
DBUG_RETURN(true);
// There is at least one empty const table
if (const_table_map != found_const_table_map)
zero_result_cause= "no matching row in const table";
DBUG_RETURN(false);
}
/**
Initialize scratch arrays for the join order optimization
@returns false if success, true if error
@note If something fails during initialization, JOIN::cleanup()
will free anything that has been partially allocated and set up.
Arrays are created in the execution mem_root, so they will be
deleted automatically when the mem_root is re-initialized.
*/
bool JOIN::init_planner_arrays()
{
// Up to one extra slot per semi-join nest is needed (if materialized)
const uint sj_nests= select_lex->sj_nests.elements;
const uint table_count= select_lex->leaf_table_count;
assert(primary_tables == 0 && tables == 0);
if (!(join_tab= alloc_jtab_array(thd, table_count)))
return true;
/*
We add 2 cells:
- because planning stage uses 0-termination so needs +1
- because after get_best_combination, we don't use 0-termination but
need +2, to host at most 2 tmp sort/group/distinct tables.
*/
if (!(best_ref= (JOIN_TAB **) thd->alloc(sizeof(JOIN_TAB *) *
(table_count + sj_nests + 2))))
return true;
// sort/group tmp tables have no map
if (!(map2table= (JOIN_TAB **) thd->alloc(sizeof(JOIN_TAB *) *
(table_count + sj_nests))))
return true;
if (!(positions= new (thd->mem_root) POSITION[table_count]))
return true;
if (!(best_positions= new (thd->mem_root) POSITION[table_count+sj_nests]))
return true;
/*
Initialize data structures for tables to be joined.
Initialize dependencies between tables.
*/
JOIN_TAB **best_ref_p= best_ref;
TABLE_LIST *tl= select_lex->leaf_tables;
for (JOIN_TAB *tab= join_tab;
tl;
tab++, tl= tl->next_leaf, best_ref_p++)
{
*best_ref_p= tab;
TABLE *const table= tl->table;
tab->table_ref= tl;
tab->set_table(table);
const int err= tl->fetch_number_of_rows();
// Initialize the cost model for the table
table->init_cost_model(cost_model());
DBUG_EXECUTE_IF("bug11747970_raise_error",
{
if (!err)
{
my_error(ER_UNKNOWN_ERROR, MYF(0));
return true;
}
});
if (err)
{
table->file->print_error(err, MYF(0));
return true;
}
table->quick_keys.clear_all();
table->possible_quick_keys.clear_all();
table->reginfo.not_exists_optimize= false;
memset(table->const_key_parts, 0, sizeof(key_part_map)*table->s->keys);
all_table_map|= tl->map();
tab->set_join(this);
tab->dependent= tl->dep_tables; // Initialize table dependencies
if (tl->schema_table)
table->file->stats.records= 2;
table->quick_condition_rows= table->file->stats.records;
tab->init_join_cond_ref(tl);
if (tl->outer_join_nest())
{
// tab belongs to a nested join, maybe to several embedding joins
tab->embedding_map= 0;
for (TABLE_LIST *embedding= tl->embedding;
embedding;
embedding= embedding->embedding)
{
NESTED_JOIN *const nested_join= embedding->nested_join;
tab->embedding_map|= nested_join->nj_map;
tab->dependent|= embedding->dep_tables;
}
}
else if (tab->join_cond())
{
// tab is the only inner table of an outer join
tab->embedding_map= 0;
for (TABLE_LIST *embedding= tl->embedding;
embedding;
embedding= embedding->embedding)
tab->embedding_map|= embedding->nested_join->nj_map;
}
tables++; // Count number of initialized tables
}
primary_tables= tables;
*best_ref_p= NULL; // Last element of array must be NULL
return false;
}
/**
Propagate dependencies between tables due to outer join relations.
@returns false if success, true if error
Build transitive closure for relation 'to be dependent on'.
This will speed up the plan search for many cases with outer joins,
as well as allow us to catch illegal cross references.
Warshall's algorithm is used to build the transitive closure.
As we may restart the outer loop upto 'table_count' times, the
complexity of the algorithm is O((number of tables)^3).
However, most of the iterations will be shortcircuited when
there are no dependencies to propagate.
*/
bool JOIN::propagate_dependencies()
{
for (uint i= 0; i < tables; i++)
{
if (!join_tab[i].dependent)
continue;
// Add my dependencies to other tables depending on me
uint j;
JOIN_TAB *tab;
for (j= 0, tab= join_tab; j < tables; j++, tab++)
{
if (tab->dependent & join_tab[i].table_ref->map())
{
const table_map was_dependent= tab->dependent;
tab->dependent|= join_tab[i].dependent;
/*
If we change dependencies for a table we already have
processed: Redo dependency propagation from this table.
*/
if (i > j && tab->dependent != was_dependent)
{
i= j-1;
break;
}
}
}
}
JOIN_TAB *const tab_end= join_tab + tables;
for (JOIN_TAB *tab= join_tab; tab < tab_end; tab++)
{
/*
Catch illegal cross references for outer joins.
This could happen before WL#2486 was implemented in 5.0, but should no
longer be possible.
Thus, an assert has been added should this happen again.
@todo Remove the error check below.
*/
assert(!(tab->dependent & tab->table_ref->map()));
if (tab->dependent & tab->table_ref->map())
{
tables= 0; // Don't use join->table
primary_tables= 0;
my_message(ER_WRONG_OUTER_JOIN, ER(ER_WRONG_OUTER_JOIN), MYF(0));
return true;
}
tab->key_dependent= tab->dependent;
}
return false;
}
/**
Extract const tables based on row counts.
@returns false if success, true if error
This extraction must be done for each execution.
Tables containing exactly zero or one rows are marked as const, but
notice the additional constraints checked below.
Tables that are extracted have their rows read before actual execution
starts and are placed in the beginning of the join_tab array.
Thus, they do not take part in join order optimization process,
which can significantly reduce the optimization time.
The data read from these tables can also be regarded as "constant"
throughout query execution, hence the column values can be used for
additional constant propagation and extraction of const tables based
on eq-ref properties.
The tables are given the type JT_SYSTEM.
*/
bool JOIN::extract_const_tables()
{
enum enum_const_table_extraction
{
extract_no_table= 0,
extract_empty_table= 1,
extract_const_table= 2
};
JOIN_TAB *const tab_end= join_tab + tables;
for (JOIN_TAB *tab= join_tab; tab < tab_end; tab++)
{
TABLE *const table= tab->table();
TABLE_LIST *const tl= tab->table_ref;
enum enum_const_table_extraction extract_method= extract_const_table;
const bool all_partitions_pruned_away= table->all_partitions_pruned_away;
if (tl->outer_join_nest())
{
/*
Table belongs to a nested join, no candidate for const table extraction.
*/
extract_method= extract_no_table;
}
else if (tl->embedding && tl->embedding->sj_cond())
{
/*
Table belongs to a semi-join.
We do not currently pull out const tables from semi-join nests.
*/
extract_method= extract_no_table;
}
else if (tab->join_cond())
{
// tab is the only inner table of an outer join, extract empty tables
extract_method= extract_empty_table;
}
switch (extract_method)
{
case extract_no_table:
break;
case extract_empty_table:
// Extract tables with zero rows, but only if statistics are exact
if ((table->file->stats.records == 0 ||
all_partitions_pruned_away) &&
(table->file->ha_table_flags() & HA_STATS_RECORDS_IS_EXACT))
mark_const_table(tab, NULL);
break;
case extract_const_table:
/*
Extract tables with zero or one rows, but do not extract tables that
1. are dependent upon other tables, or
2. have no exact statistics, or
3. are full-text searched
*/
if ((table->s->system ||
table->file->stats.records <= 1 ||
all_partitions_pruned_away) &&
!tab->dependent && // 1
(table->file->ha_table_flags() & HA_STATS_RECORDS_IS_EXACT) && // 2
!table->fulltext_searched) // 3
mark_const_table(tab, NULL);
break;
}
}
// Read const tables (tables matching no more than 1 rows)
if (!const_tables)
return false;
for (POSITION *p_pos= positions, *p_end= p_pos + const_tables;
p_pos < p_end;
p_pos++)
{
JOIN_TAB *const tab= p_pos->table;
const int status= join_read_const_table(tab, p_pos);
if (status > 0)
return true;
else if (status == 0)
{
found_const_table_map|= tab->table_ref->map();
tab->table_ref->optimized_away= true;
}
}
return false;
}
/**
Extract const tables based on functional dependencies.
@returns false if success, true if error
This extraction must be done for each execution.
Mark as const the tables that
- are functionally dependent on constant values, or
- are inner tables of an outer join and contain exactly zero or one rows
Tables that are extracted have their rows read before actual execution
starts and are placed in the beginning of the join_tab array, just as
described for JOIN::extract_const_tables().
The tables are given the type JT_CONST.
*/
bool JOIN::extract_func_dependent_tables()
{
// loop until no more const tables are found
bool ref_changed;
table_map found_ref;
do
{
more_const_tables_found:
ref_changed = false;
found_ref= 0;
// Loop over all tables that are not already determined to be const
for (JOIN_TAB **pos= best_ref + const_tables; *pos; pos++)
{
JOIN_TAB *const tab= *pos;
TABLE *const table= tab->table();
TABLE_LIST *const tl= tab->table_ref;
/*
If equi-join condition by a key is null rejecting and after a
substitution of a const table the key value happens to be null
then we can state that there are no matches for this equi-join.
*/
Key_use *keyuse= tab->keyuse();
if (keyuse && tab->join_cond() && !tab->embedding_map)
{
/*
When performing an outer join operation if there are no matching rows
for the single row of the outer table all the inner tables are to be
null complemented and thus considered as constant tables.
Here we apply this consideration to the case of outer join operations
with a single inner table only because the case with nested tables
would require a more thorough analysis.
TODO. Apply single row substitution to null complemented inner tables
for nested outer join operations.
*/
while (keyuse->table_ref == tl)
{
if (!(keyuse->val->used_tables() & ~const_table_map) &&
keyuse->val->is_null() && keyuse->null_rejecting)
{
table->set_null_row();
found_const_table_map|= tl->map();
mark_const_table(tab, keyuse);
goto more_const_tables_found;
}
keyuse++;
}
}
if (tab->dependent) // If dependent on some table
{
// All dependent tables must be const
if (tab->dependent & ~const_table_map)
continue;
/*
Mark a dependent table as constant if
1. it has exactly zero or one rows (it is a system table), and
2. it is not within a nested outer join, and
3. it does not have an expensive outer join condition.
This is because we have to determine whether an outer-joined table
has a real row or a null-extended row in the optimizer phase.
We have no possibility to evaluate its join condition at
execution time, when it is marked as a system table.
*/
if (table->file->stats.records <= 1L && // 1
(table->file->ha_table_flags() & HA_STATS_RECORDS_IS_EXACT) && // 1
!tl->outer_join_nest() && // 2
!(tab->join_cond() && tab->join_cond()->is_expensive())) // 3
{ // system table
mark_const_table(tab, NULL);
const int status=
join_read_const_table(tab, positions + const_tables - 1);
if (status > 0)
return true;
else if (status == 0)
found_const_table_map|= tl->map();
continue;
}
}
// Check if table can be read by key or table only uses const refs
if ((keyuse= tab->keyuse()))
{
while (keyuse->table_ref == tl)
{
Key_use *const start_keyuse= keyuse;
const uint key= keyuse->key;
tab->keys().set_bit(key); // QQ: remove this ?
table_map refs= 0;
key_map const_ref, eq_part;
do
{
if (keyuse->val->type() != Item::NULL_ITEM && !keyuse->optimize)
{
if (!((~found_const_table_map) & keyuse->used_tables))
const_ref.set_bit(keyuse->keypart);
else
refs|= keyuse->used_tables;
eq_part.set_bit(keyuse->keypart);
}
keyuse++;
} while (keyuse->table_ref == tl && keyuse->key == key);
/*
Extract const tables with proper key dependencies.
Exclude tables that
1. are full-text searched, or
2. are part of nested outer join, or
3. are part of semi-join, or
4. have an expensive outer join condition.
5. are blocked by handler for const table optimize.
*/
if (eq_part.is_prefix(table->key_info[key].user_defined_key_parts) &&
!table->fulltext_searched && // 1
!tl->outer_join_nest() && // 2
!(tl->embedding && tl->embedding->sj_cond()) && // 3
!(tab->join_cond() && tab->join_cond()->is_expensive()) &&// 4
!(table->file->ha_table_flags() & HA_BLOCK_CONST_TABLE)) // 5
{
if (table->key_info[key].flags & HA_NOSAME)
{
if (const_ref == eq_part)
{ // Found everything for ref.
ref_changed = true;
mark_const_table(tab, start_keyuse);
if (create_ref_for_key(this, tab, start_keyuse,
found_const_table_map))
return true;
const int status=
join_read_const_table(tab, positions + const_tables - 1);
if (status > 0)
return true;
else if (status == 0)
found_const_table_map|= tl->map();
break;
}
else
found_ref|= refs; // Table is const if all refs are const
}
else if (const_ref == eq_part)
tab->const_keys.set_bit(key);
}
}
}
}
} while ((const_table_map & found_ref) && ref_changed);
return false;
}
/**
Update info on indexes that can be used for search lookups as
reading const tables may has added new sargable predicates.
*/
void JOIN::update_sargable_from_const(SARGABLE_PARAM *sargables)
{
for ( ; sargables->field; sargables++)
{
Field *const field= sargables->field;
JOIN_TAB *const tab= field->table->reginfo.join_tab;
key_map possible_keys= field->key_start;
possible_keys.intersect(field->table->keys_in_use_for_query);
bool is_const= true;
for (uint j= 0; j < sargables->num_values; j++)
is_const&= sargables->arg_value[j]->const_item();
if (is_const)
{
tab->const_keys.merge(possible_keys);
tab->keys().merge(possible_keys);
}
}
}
/**
Estimate the number of matched rows for each joined table.
Set up range scan for tables that have proper predicates.
@returns false if success, true if error
*/
bool JOIN::estimate_rowcount()
{
Opt_trace_context *const trace= &thd->opt_trace;
Opt_trace_object trace_wrapper(trace);
Opt_trace_array trace_records(trace, "rows_estimation");
JOIN_TAB *const tab_end= join_tab + tables;
for (JOIN_TAB *tab= join_tab; tab < tab_end; tab++)
{
const Cost_model_table *const cost_model= tab->table()->cost_model();
Opt_trace_object trace_table(trace);
trace_table.add_utf8_table(tab->table_ref);
if (tab->type() == JT_SYSTEM || tab->type() == JT_CONST)
{
trace_table.add("rows", 1).add("cost", 1)
.add_alnum("table_type", (tab->type() == JT_SYSTEM) ? "system": "const")
.add("empty", tab->table()->has_null_row());
// Only one matching row and one block to read
tab->set_records(tab->found_records= 1);
tab->worst_seeks= cost_model->page_read_cost(1.0);
tab->read_time= static_cast<ha_rows>(tab->worst_seeks);
continue;
}
// Approximate number of found rows and cost to read them
tab->set_records(tab->found_records= tab->table()->file->stats.records);
const Cost_estimate table_scan_time= tab->table()->file->table_scan_cost();
tab->read_time= static_cast<ha_rows>(table_scan_time.total_cost());
/*
Set a max value for the cost of seek operations we can expect
when using key lookup. This can't be too high as otherwise we
are likely to use table scan.
*/
tab->worst_seeks=
min(cost_model->page_read_cost((double) tab->found_records / 10),
(double) tab->read_time * 3);
const double min_worst_seek= cost_model->page_read_cost(2.0);
if (tab->worst_seeks < min_worst_seek) // Fix for small tables
tab->worst_seeks= min_worst_seek;
/*
Add to tab->const_keys those indexes for which all group fields or
all select distinct fields participate in one index.
*/
add_group_and_distinct_keys(this, tab);
/*
Perform range analysis if there are keys it could use (1).
Don't do range analysis if on the inner side of an outer join (2).
Do range analysis if on the inner side of a semi-join (3).
*/
TABLE_LIST *const tl= tab->table_ref;
if (!tab->const_keys.is_clear_all() && // (1)
(!tl->embedding || // (2)
(tl->embedding && tl->embedding->sj_cond()))) // (3)
{
/*
This call fills tab->quick() with the best QUICK access method
possible for this table, and only if it's better than table scan.
It also fills tab->needed_reg.
*/
ha_rows records= get_quick_record_count(thd, tab, row_limit);
if (records == 0 && thd->is_error())
return true;
/*
Check for "impossible range", but make sure that we do not attempt
to mark semi-joined tables as "const" (only semi-joined tables that
are functionally dependent can be marked "const", and subsequently
pulled out of their semi-join nests).
*/
if (records == 0 &&
tab->table()->reginfo.impossible_range &&
(!(tl->embedding && tl->embedding->sj_cond())))
{
/*
Impossible WHERE condition or join condition
In case of join cond, mark that one empty NULL row is matched.
In case of WHERE, don't set found_const_table_map to get the
caller to abort with a zero row result.
*/
mark_const_table(tab, NULL);
tab->set_type(JT_CONST); // Override setting made in mark_const_table()
if (tab->join_cond())
{
// Generate an empty row
trace_table.add("returning_empty_null_row", true).
add_alnum("cause", "impossible_on_condition");
found_const_table_map|= tl->map();
tab->table()->set_null_row(); // All fields are NULL
}
else
{
trace_table.add("rows", 0).
add_alnum("cause", "impossible_where_condition");
}
}
if (records != HA_POS_ERROR)
{
tab->found_records= records;
tab->read_time= (ha_rows) (tab->quick() ?
tab->quick()->cost_est.total_cost() : 0.0);
}
}
else
{
Opt_trace_object(trace, "table_scan").
add("rows", tab->found_records).
add("cost", tab->read_time);
}
}
return false;
}
/**
Set semi-join embedding join nest pointers.
Set pointer to embedding semi-join nest for all semi-joined tables.
Note that this must be done for every table inside all semi-join nests,
even for tables within outer join nests embedded in semi-join nests.
A table can never be part of multiple semi-join nests, hence no
ambiguities can ever occur.
Note also that the pointer is not set for TABLE_LIST objects that
are outer join nests within semi-join nests.
*/
void JOIN::set_semijoin_embedding()
{
assert(!select_lex->sj_nests.is_empty());
JOIN_TAB *const tab_end= join_tab + primary_tables;
for (JOIN_TAB *tab= join_tab; tab < tab_end; tab++)
{
for (TABLE_LIST *tl= tab->table_ref; tl->embedding; tl= tl->embedding)
{
if (tl->embedding->sj_cond())
{
tab->emb_sj_nest= tl->embedding;
break;
}
}
}
}
/**
@brief Check if semijoin's compared types allow materialization.
@param[inout] sj_nest Semi-join nest containing information about correlated
expressions. Set nested_join->sjm.scan_allowed to TRUE if
MaterializeScan strategy allowed. Set nested_join->sjm.lookup_allowed
to TRUE if MaterializeLookup strategy allowed
@details
This is a temporary fix for BUG#36752.
There are two subquery materialization strategies for semijoin:
1. Materialize and do index lookups in the materialized table. See
BUG#36752 for description of restrictions we need to put on the
compared expressions.
In addition, since indexes are not supported for BLOB columns,
this strategy can not be used if any of the columns in the
materialized table will be BLOB/GEOMETRY columns. (Note that
also columns for non-BLOB values that may be greater in size
than CONVERT_IF_BIGGER_TO_BLOB, will be represented as BLOB
columns.)
2. Materialize and then do a full scan of the materialized table.
The same criteria as for MaterializeLookup are applied, except that
BLOB/GEOMETRY columns are allowed.
*/
static
void semijoin_types_allow_materialization(TABLE_LIST *sj_nest)
{
DBUG_ENTER("semijoin_types_allow_materialization");
assert(sj_nest->nested_join->sj_outer_exprs.elements ==
sj_nest->nested_join->sj_inner_exprs.elements);
if (sj_nest->nested_join->sj_outer_exprs.elements > MAX_REF_PARTS)
{
sj_nest->nested_join->sjm.scan_allowed= false;
sj_nest->nested_join->sjm.lookup_allowed= false;
DBUG_VOID_RETURN;
}
List_iterator<Item> it1(sj_nest->nested_join->sj_outer_exprs);
List_iterator<Item> it2(sj_nest->nested_join->sj_inner_exprs);
sj_nest->nested_join->sjm.scan_allowed= true;
sj_nest->nested_join->sjm.lookup_allowed= true;
bool blobs_involved= false;
Item *outer, *inner;
uint total_lookup_index_length= 0;
uint max_key_length;
uint max_key_part_length;
/*
Maximum lengths for keys and key parts that are supported by
the temporary table storage engine(s).
*/
get_max_key_and_part_length(&max_key_length,
&max_key_part_length);
while (outer= it1++, inner= it2++)
{
assert(outer->real_item() && inner->real_item());
if (!types_allow_materialization(outer, inner))
{
sj_nest->nested_join->sjm.scan_allowed= false;
sj_nest->nested_join->sjm.lookup_allowed= false;
DBUG_VOID_RETURN;
}
blobs_involved|= inner->is_blob_field();
// Calculate the index length of materialized table
const uint lookup_index_length= get_key_length_tmp_table(inner);
if (lookup_index_length > max_key_part_length)
sj_nest->nested_join->sjm.lookup_allowed= false;
total_lookup_index_length+= lookup_index_length ;
}
if (total_lookup_index_length > max_key_length)
sj_nest->nested_join->sjm.lookup_allowed= false;
if (blobs_involved)
sj_nest->nested_join->sjm.lookup_allowed= false;
if (sj_nest->embedding)
{
assert(sj_nest->embedding->join_cond_optim());
/*
There are two issues that prevent materialization strategy from being
used when a semi-join nest is on the inner side of an outer join:
1. If the semi-join contains dependencies to outer tables,
materialize-scan strategy cannot be used.
2. Make sure that executor is able to evaluate triggered conditions
for semi-join materialized tables. It should be correct, but needs
verification.
TODO: Remove this limitation!
Handle this by disabling materialization strategies:
*/
sj_nest->nested_join->sjm.scan_allowed= false;
sj_nest->nested_join->sjm.lookup_allowed= false;
DBUG_VOID_RETURN;
}
DBUG_PRINT("info",("semijoin_types_allow_materialization: ok, allowed"));
DBUG_VOID_RETURN;
}
/*****************************************************************************
Create JOIN_TABS, make a guess about the table types,
Approximate how many records will be used in each table
*****************************************************************************/
/**
Returns estimated number of rows that could be fetched by given
access method.
The function calls the range optimizer to estimate the cost of the
cheapest QUICK_* index access method to scan one or several of the
'keys' using the conditions 'select->cond'. The range optimizer
compares several different types of 'quick select' methods (range
scan, index merge, loose index scan) and selects the cheapest one.
If the best index access method is cheaper than a table- and an index
scan, then the range optimizer also constructs the corresponding
QUICK_* object and assigns it to select->quick. In most cases this
is the QUICK_* object used at later (optimization and execution)
phases.
@param thd Session that runs the query.
@param tab JOIN_TAB of source table.
@param limit maximum number of rows to select.
@note
In case of valid range, a QUICK_SELECT_I object will be constructed and
saved in select->quick.
@return Estimated number of result rows selected from 'tab'.
@retval HA_POS_ERROR For derived tables/views or if an error occur.
@retval 0 If impossible query (i.e. certainly no rows will be
selected.)
*/
static ha_rows get_quick_record_count(THD *thd, JOIN_TAB *tab, ha_rows limit)
{
DBUG_ENTER("get_quick_record_count");
uchar buff[STACK_BUFF_ALLOC];
if (check_stack_overrun(thd, STACK_MIN_SIZE, buff))
DBUG_RETURN(0); // Fatal error flag is set
TABLE_LIST *const tl= tab->table_ref;
// Derived tables aren't filled yet, so no stats are available.
if (!tl->uses_materialization())
{
QUICK_SELECT_I *qck;
int error= test_quick_select(thd,
tab->const_keys,
0, //empty table_map
limit,
false, //don't force quick range
ORDER::ORDER_NOT_RELEVANT, tab,
tab->join_cond() ? tab->join_cond() :
tab->join()->where_cond,
&tab->needed_reg, &qck, tab->table()->force_index);
tab->set_quick(qck);
if (error == 1)
DBUG_RETURN(qck->records);
if (error == -1)
{
tl->table->reginfo.impossible_range=1;
DBUG_RETURN(0);
}
DBUG_PRINT("warning",("Couldn't use record count on const keypart"));
}
else if (tl->materializable_is_const())
{
DBUG_RETURN(tl->derived_unit()->query_result()->estimated_rowcount);
}
DBUG_RETURN(HA_POS_ERROR);
}
/*
Get estimated record length for semi-join materialization temptable
SYNOPSIS
get_tmp_table_rec_length()
items IN subquery's select list.
DESCRIPTION
Calculate estimated record length for semi-join materialization
temptable. It's an estimate because we don't follow every bit of
create_tmp_table()'s logic. This isn't necessary as the return value of
this function is used only for cost calculations.
RETURN
Length of the temptable record, in bytes
*/
static uint get_tmp_table_rec_length(List<Item> &items)
{
uint len= 0;
Item *item;
List_iterator<Item> it(items);
while ((item= it++))
{
switch (item->result_type()) {
case REAL_RESULT:
len += sizeof(double);
break;
case INT_RESULT:
if (item->max_length >= (MY_INT32_NUM_DECIMAL_DIGITS - 1))
len += 8;
else
len += 4;
break;
case STRING_RESULT:
/* DATE/TIME and GEOMETRY fields have STRING_RESULT result type. */
if (item->is_temporal() || item->field_type() == MYSQL_TYPE_GEOMETRY)
len += 8;
else
len += item->max_length;
break;
case DECIMAL_RESULT:
len += 10;
break;
case ROW_RESULT:
default:
assert(0); /* purecov: deadcode */
break;
}
}
return len;
}
/**
Writes to the optimizer trace information about dependencies between
tables.
@param trace optimizer trace
@param join_tabs all JOIN_TABs of the join
@param table_count how many JOIN_TABs in the 'join_tabs' array
*/
static void trace_table_dependencies(Opt_trace_context * trace,
JOIN_TAB *join_tabs,
uint table_count)
{
Opt_trace_object trace_wrapper(trace);
Opt_trace_array trace_dep(trace, "table_dependencies");
for (uint i= 0 ; i < table_count ; i++)
{
TABLE_LIST *table_ref= join_tabs[i].table_ref;
Opt_trace_object trace_one_table(trace);
trace_one_table.add_utf8_table(table_ref).
add("row_may_be_null", table_ref->table->is_nullable());
const table_map map= table_ref->map();
assert(map < (1ULL << table_count));
for (uint j= 0; j < table_count; j++)
{
if (map & (1ULL << j))
{
trace_one_table.add("map_bit", j);
break;
}
}
Opt_trace_array depends_on(trace, "depends_on_map_bits");
// RAND_TABLE_BIT may be in join_tabs[i].dependent, so we test all 64 bits
compile_time_assert(sizeof(table_ref->map()) <= 64);
for (uint j= 0; j < 64; j++)
{
if (join_tabs[i].dependent & (1ULL << j))
depends_on.add(j);
}
}
}
/**
Add to join_tab[i]->condition() "table.field IS NOT NULL" conditions
we've inferred from ref/eq_ref access performed.
This function is a part of "Early NULL-values filtering for ref access"
optimization.
Example of this optimization:
For query SELECT * FROM t1,t2 WHERE t2.key=t1.field @n
and plan " any-access(t1), ref(t2.key=t1.field) " @n
add "t1.field IS NOT NULL" to t1's table condition. @n
Description of the optimization:
We look through equalities choosen to perform ref/eq_ref access,
pick equalities that have form "tbl.part_of_key = othertbl.field"
(where othertbl is a non-const table and othertbl.field may be NULL)
and add them to conditions on correspoding tables (othertbl in this
example).
Exception from that is the case when referred_tab->join != join.
I.e. don't add NOT NULL constraints from any embedded subquery.
Consider this query:
@code
SELECT A.f2 FROM t1 LEFT JOIN t2 A ON A.f2 = f1
WHERE A.f3=(SELECT MIN(f3) FROM t2 C WHERE A.f4 = C.f4) OR A.f3 IS NULL;
@endcode
Here condition A.f3 IS NOT NULL is going to be added to the WHERE
condition of the embedding query.
Another example:
SELECT * FROM t10, t11 WHERE (t10.a < 10 OR t10.a IS NULL)
AND t11.b <=> t10.b AND (t11.a = (SELECT MAX(a) FROM t12
WHERE t12.b = t10.a ));
Here condition t10.a IS NOT NULL is going to be added.
In both cases addition of NOT NULL condition will erroneously reject
some rows of the result set.
referred_tab->join != join constraint would disallow such additions.
This optimization doesn't affect the choices that ref, range, or join
optimizer make. This was intentional because this was added after 4.1
was GA.
Implementation overview
1. update_ref_and_keys() accumulates info about null-rejecting
predicates in in Key_field::null_rejecting
1.1 add_key_part saves these to Key_use.
2. create_ref_for_key copies them to TABLE_REF.
3. add_not_null_conds adds "x IS NOT NULL" to join_tab->m_condition of
appropiate JOIN_TAB members.
*/
static void add_not_null_conds(JOIN *join)
{
DBUG_ENTER("add_not_null_conds");
ASSERT_BEST_REF_IN_JOIN_ORDER(join);
for (uint i=join->const_tables ; i < join->tables ; i++)
{
JOIN_TAB *const tab= join->best_ref[i];
if ((tab->type() == JT_REF || tab->type() == JT_EQ_REF ||
tab->type() == JT_REF_OR_NULL) &&
!tab->table()->is_nullable())
{
for (uint keypart= 0; keypart < tab->ref().key_parts; keypart++)
{
if (tab->ref().null_rejecting & ((key_part_map)1 << keypart))
{
Item *item= tab->ref().items[keypart];
Item *notnull;
Item *real= item->real_item();
assert(real->type() == Item::FIELD_ITEM);
Item_field *not_null_item= (Item_field*)real;
JOIN_TAB *referred_tab= not_null_item->field->table->reginfo.join_tab;
/*
For UPDATE queries such as:
UPDATE t1 SET t1.f2=(SELECT MAX(t2.f4) FROM t2 WHERE t2.f3=t1.f1);
not_null_item is the t1.f1, but it's referred_tab is 0.
*/
if (!referred_tab || referred_tab->join() != join)
continue;
if (!(notnull= new Item_func_isnotnull(not_null_item)))
DBUG_VOID_RETURN;
/*
We need to do full fix_fields() call here in order to have correct
notnull->const_item(). This is needed e.g. by test_quick_select
when it is called from make_join_select after this function is
called.
*/
if (notnull->fix_fields(join->thd, ¬null))
DBUG_VOID_RETURN;
DBUG_EXECUTE("where",print_where(notnull,
referred_tab->table()->alias,
QT_ORDINARY););
referred_tab->and_with_condition(notnull);
}
}
}
}
DBUG_VOID_RETURN;
}
/**
Check if given expression only uses fields covered by index #keyno in the
table tbl. The expression can use any fields in any other tables.
The expression is guaranteed not to be AND or OR - those constructs are
handled outside of this function.
Restrict some function types from being pushed down to storage engine:
a) Don't push down the triggered conditions. Nested outer joins execution
code may need to evaluate a condition several times (both triggered and
untriggered).
b) Stored functions contain a statement that might start new operations (like
DML statements) from within the storage engine. This does not work against
all SEs.
c) Subqueries might contain nested subqueries and involve more tables.
@param item Expression to check
@param tbl The table having the index
@param keyno The index number
@param other_tbls_ok TRUE <=> Fields of other non-const tables are allowed
@return false if No, true if Yes
*/
bool uses_index_fields_only(Item *item, TABLE *tbl, uint keyno,
bool other_tbls_ok)
{
// Restrictions b and c.
if (item->has_stored_program() || item->has_subquery())
return false;
if (item->const_item())
return true;
const Item::Type item_type= item->type();
switch (item_type) {
case Item::FUNC_ITEM:
{
Item_func *item_func= (Item_func*)item;
const Item_func::Functype func_type= item_func->functype();
/*
Restriction a.
TODO: Consider cloning the triggered condition and using the copies
for:
1. push the first copy down, to have most restrictive index condition
possible.
2. Put the second copy into tab->m_condition.
*/
if (func_type == Item_func::TRIG_COND_FUNC)
return false;
/* This is a function, apply condition recursively to arguments */
if (item_func->argument_count() > 0)
{
Item **item_end= (item_func->arguments()) + item_func->argument_count();
for (Item **child= item_func->arguments(); child != item_end; child++)
{
if (!uses_index_fields_only(*child, tbl, keyno, other_tbls_ok))
return FALSE;
}
}
return TRUE;
}
case Item::COND_ITEM:
{
/*
This is a AND/OR condition. Regular AND/OR clauses are handled by
make_cond_for_index() which will chop off the part that can be
checked with index. This code is for handling non-top-level AND/ORs,
e.g. func(x AND y).
*/
List_iterator<Item> li(*((Item_cond*)item)->argument_list());
Item *item;
while ((item=li++))
{
if (!uses_index_fields_only(item, tbl, keyno, other_tbls_ok))
return FALSE;
}
return TRUE;
}
case Item::FIELD_ITEM:
{
Item_field *item_field= (Item_field*)item;
if (item_field->field->table != tbl)
return other_tbls_ok;
/*
The below is probably a repetition - the first part checks the
other two, but let's play it safe:
*/
return item_field->field->part_of_key.is_set(keyno) &&
item_field->field->type() != MYSQL_TYPE_GEOMETRY &&
item_field->field->type() != MYSQL_TYPE_BLOB;
}
case Item::REF_ITEM:
return uses_index_fields_only(item->real_item(), tbl, keyno,
other_tbls_ok);
default:
return FALSE; /* Play it safe, don't push unknown non-const items */
}
}
/**
Optimize semi-join nests that could be run with sj-materialization
@param join The join to optimize semi-join nests for
@details
Optimize each of the semi-join nests that can be run with
materialization. For each of the nests, we
- Generate the best join order for this "sub-join" and remember it;
- Remember the sub-join execution cost (it's part of materialization
cost);
- Calculate other costs that will be incurred if we decide
to use materialization strategy for this semi-join nest.
All obtained information is saved and will be used by the main join
optimization pass.
@return false if successful, true if error
*/
static bool optimize_semijoin_nests_for_materialization(JOIN *join)
{
DBUG_ENTER("optimize_semijoin_nests_for_materialization");
List_iterator<TABLE_LIST> sj_list_it(join->select_lex->sj_nests);
TABLE_LIST *sj_nest;
Opt_trace_context * const trace= &join->thd->opt_trace;
while ((sj_nest= sj_list_it++))
{
/* As a precaution, reset pointers that were used in prior execution */
sj_nest->nested_join->sjm.positions= NULL;
/* Calculate the cost of materialization if materialization is allowed. */
if (sj_nest->nested_join->sj_enabled_strategies &
OPTIMIZER_SWITCH_MATERIALIZATION)
{
/* A semi-join nest should not contain tables marked as const */
assert(!(sj_nest->sj_inner_tables & join->const_table_map));
Opt_trace_object trace_wrapper(trace);
Opt_trace_object
trace_sjmat(trace, "execution_plan_for_potential_materialization");
Opt_trace_array trace_sjmat_steps(trace, "steps");
/*
Try semijoin materialization if the semijoin is classified as
non-trivially-correlated.
*/
if (sj_nest->nested_join->sj_corr_tables)
continue;
/*
Check whether data types allow execution with materialization.
*/
semijoin_types_allow_materialization(sj_nest);
if (!sj_nest->nested_join->sjm.scan_allowed &&
!sj_nest->nested_join->sjm.lookup_allowed)
continue;
if (Optimize_table_order(join->thd, join, sj_nest).choose_table_order())
DBUG_RETURN(true);
const uint n_tables= my_count_bits(sj_nest->sj_inner_tables);
calculate_materialization_costs(join, sj_nest, n_tables,
&sj_nest->nested_join->sjm);
/*
Cost data is in sj_nest->nested_join->sjm. We also need to save the
plan:
*/
if (!(sj_nest->nested_join->sjm.positions=
(st_position*)join->thd->alloc(sizeof(st_position)*n_tables)))
DBUG_RETURN(true);
memcpy(sj_nest->nested_join->sjm.positions,
join->best_positions + join->const_tables,
sizeof(st_position) * n_tables);
}
}
DBUG_RETURN(false);
}
/*
Check if table's Key_use elements have an eq_ref(outer_tables) candidate
SYNOPSIS
find_eq_ref_candidate()
tl Table to be checked
sj_inner_tables Bitmap of inner tables. eq_ref(inner_table) doesn't
count.
DESCRIPTION
Check if table's Key_use elements have an eq_ref(outer_tables) candidate
TODO
Check again if it is feasible to factor common parts with constant table
search
RETURN
TRUE - There exists an eq_ref(outer-tables) candidate
FALSE - Otherwise
*/
static bool find_eq_ref_candidate(TABLE_LIST *tl, table_map sj_inner_tables)
{
Key_use *keyuse= tl->table->reginfo.join_tab->keyuse();
if (keyuse)
{
while (1) /* For each key */
{
const uint key= keyuse->key;
KEY *const keyinfo= tl->table->key_info + key;
key_part_map bound_parts= 0;
if ((keyinfo->flags & (HA_NOSAME)) == HA_NOSAME)
{
do /* For all equalities on all key parts */
{
/* Check if this is "t.keypart = expr(outer_tables) */
if (!(keyuse->used_tables & sj_inner_tables) &&
!(keyuse->optimize & KEY_OPTIMIZE_REF_OR_NULL))
{
/*
Consider only if the resulting condition does not pass a NULL
value through. Especially needed for a UNIQUE index on NULLable
columns where a duplicate row is possible with NULL values.
*/
if (keyuse->null_rejecting || !keyuse->val->maybe_null ||
!keyinfo->key_part[keyuse->keypart].field->maybe_null())
bound_parts|= (key_part_map)1 << keyuse->keypart;
}
keyuse++;
} while (keyuse->key == key && keyuse->table_ref == tl);
if (bound_parts == LOWER_BITS(uint, keyinfo->user_defined_key_parts))
return true;
if (keyuse->table_ref != tl)
return false;
}
else
{
do
{
keyuse++;
if (keyuse->table_ref != tl)
return false;
}
while (keyuse->key == key);
}
}
}
return false;
}
/**
Pull tables out of semi-join nests based on functional dependencies
@param join The join where to do the semi-join table pullout
@return False if successful, true if error (Out of memory)
@details
Pull tables out of semi-join nests based on functional dependencies,
ie. if a table is accessed via eq_ref(outer_tables).
The function may be called several times, the caller is responsible
for setting up proper key information that this function acts upon.
PRECONDITIONS
When this function is called, the join may have several semi-join nests
but it is guaranteed that one semi-join nest does not contain another.
For functionally dependent tables to be pulled out, key information must
have been calculated (see update_ref_and_keys()).
POSTCONDITIONS
* Tables that were pulled out are removed from the semi-join nest they
belonged to and added to the parent join nest.
* For these tables, the used_tables and not_null_tables fields of
the semi-join nest they belonged to will be adjusted.
The semi-join nest is also marked as correlated, and
sj_corr_tables and sj_depends_on are adjusted if necessary.
* Semi-join nests' sj_inner_tables is set equal to used_tables
NOTE
Table pullout may make uncorrelated subquery correlated. Consider this
example:
... WHERE oe IN (SELECT it1.primary_key WHERE p(it1, it2) ... )
here table it1 can be pulled out (we have it1.primary_key=oe which gives
us functional dependency). Once it1 is pulled out, all references to it1
from p(it1, it2) become references to outside of the subquery and thus
make the subquery (i.e. its semi-join nest) correlated.
Making the subquery (i.e. its semi-join nest) correlated prevents us from
using Materialization or LooseScan to execute it.
*/
static bool pull_out_semijoin_tables(JOIN *join)
{
TABLE_LIST *sj_nest;
DBUG_ENTER("pull_out_semijoin_tables");
assert(!join->select_lex->sj_nests.is_empty());
List_iterator<TABLE_LIST> sj_list_it(join->select_lex->sj_nests);
Opt_trace_context * const trace= &join->thd->opt_trace;
Opt_trace_object trace_wrapper(trace);
Opt_trace_array trace_pullout(trace, "pulled_out_semijoin_tables");
/* Try pulling out tables from each semi-join nest */
while ((sj_nest= sj_list_it++))
{
table_map pulled_tables= 0;
List_iterator<TABLE_LIST> child_li(sj_nest->nested_join->join_list);
TABLE_LIST *tbl;
/*
Calculate set of tables within this semi-join nest that have
other dependent tables
*/
table_map dep_tables= 0;
while ((tbl= child_li++))
{
TABLE *const table= tbl->table;
if (table &&
(table->reginfo.join_tab->dependent &
sj_nest->nested_join->used_tables))
dep_tables|= table->reginfo.join_tab->dependent;
}
/*
Find which tables we can pull out based on key dependency data.
Note that pulling one table out can allow us to pull out some
other tables too.
*/
bool pulled_a_table;
do
{
pulled_a_table= FALSE;
child_li.rewind();
while ((tbl= child_li++))
{
if (tbl->table &&
!(pulled_tables & tbl->map()) &&
!(dep_tables & tbl->map()))
{
if (find_eq_ref_candidate(tbl,
sj_nest->nested_join->used_tables &
~pulled_tables))
{
pulled_a_table= TRUE;
pulled_tables |= tbl->map();
Opt_trace_object(trace).add_utf8_table(tbl).
add("functionally_dependent", true);
/*
Pulling a table out of uncorrelated subquery in general makes
it correlated. See the NOTE to this function.
*/
sj_nest->nested_join->sj_corr_tables|= tbl->map();
sj_nest->nested_join->sj_depends_on|= tbl->map();
}
}
}
} while (pulled_a_table);
child_li.rewind();
/*
Move the pulled out TABLE_LIST elements to the parents.
*/
sj_nest->nested_join->used_tables&= ~pulled_tables;
sj_nest->nested_join->not_null_tables&= ~pulled_tables;
/* sj_inner_tables is a copy of nested_join->used_tables */
sj_nest->sj_inner_tables= sj_nest->nested_join->used_tables;
if (pulled_tables)
{
List<TABLE_LIST> *upper_join_list= (sj_nest->embedding != NULL) ?
&sj_nest->embedding->nested_join->join_list :
&join->select_lex->top_join_list;
Prepared_stmt_arena_holder ps_arena_holder(join->thd);
while ((tbl= child_li++))
{
if (tbl->table &&
!(sj_nest->nested_join->used_tables & tbl->map()))
{
/*
Pull the table up in the same way as simplify_joins() does:
update join_list and embedding pointers but keep next[_local]
pointers.
*/
child_li.remove();
if (upper_join_list->push_back(tbl))
DBUG_RETURN(TRUE);
tbl->join_list= upper_join_list;
tbl->embedding= sj_nest->embedding;
}
}
/* Remove the sj-nest itself if we've removed everything from it */
if (!sj_nest->nested_join->used_tables)
{
List_iterator<TABLE_LIST> li(*upper_join_list);
/* Find the sj_nest in the list. */
while (sj_nest != li++)
{}
li.remove();
/* Also remove it from the list of SJ-nests: */
sj_list_it.remove();
}
}
}
DBUG_RETURN(FALSE);
}
/**
@defgroup RefOptimizerModule Ref Optimizer
@{
This module analyzes all equality predicates to determine the best
independent ref/eq_ref/ref_or_null index access methods.
The 'ref' optimizer determines the columns (and expressions over them) that
reference columns in other tables via an equality, and analyzes which keys
and key parts can be used for index lookup based on these references. The
main outcomes of the 'ref' optimizer are:
- A bi-directional graph of all equi-join conditions represented as an
array of Key_use elements. This array is stored in JOIN::keyuse_array in
table, key, keypart order. Each JOIN_TAB::keyuse points to the
first Key_use element with the same table as JOIN_TAB::table.
- The table dependencies needed by the optimizer to determine what
tables must be before certain table so that they provide the
necessary column bindings for the equality predicates.
- Computed properties of the equality predicates such as null_rejecting
and the result size of each separate condition.
Updates in JOIN_TAB:
- JOIN_TAB::keys Bitmap of all used keys.
- JOIN_TAB::const_keys Bitmap of all keys that may be used with quick_select.
- JOIN_TAB::keyuse Pointer to possible keys.
*/
/**
A Key_field is a descriptor of a predicate of the form (column <op> val).
Currently 'op' is one of {'=', '<=>', 'IS [NOT] NULL', 'arg1 IN arg2'},
and 'val' can be either another column or an expression (including constants).
Key_field's are used to analyze columns that may potentially serve as
parts of keys for index lookup. If 'field' is part of an index, then
add_key_part() creates a corresponding Key_use object and inserts it
into the JOIN::keyuse_array which is passed by update_ref_and_keys().
The structure is used only during analysis of the candidate columns for
index 'ref' access.
*/
struct Key_field {
Key_field(Item_field *item_field, Item *val, uint level,
uint optimize, bool eq_func,
bool null_rejecting, bool *cond_guard, uint sj_pred_no)
: item_field(item_field), val(val), level(level),
optimize(optimize), eq_func(eq_func),
null_rejecting(null_rejecting), cond_guard(cond_guard),
sj_pred_no(sj_pred_no)
{}
Item_field *item_field; ///< Item representing the column
Item *val; ///< May be empty if diff constant
uint level;
uint optimize; ///< KEY_OPTIMIZE_*
bool eq_func;
/**
If true, the condition this struct represents will not be satisfied
when val IS NULL.
@sa Key_use::null_rejecting .
*/
bool null_rejecting;
bool *cond_guard; ///< @sa Key_use::cond_guard
uint sj_pred_no; ///< @sa Key_use::sj_pred_no
};
/* Values in optimize */
#define KEY_OPTIMIZE_EXISTS 1
#define KEY_OPTIMIZE_REF_OR_NULL 2
/**
Merge new key definitions to old ones, remove those not used in both.
This is called for OR between different levels.
To be able to do 'ref_or_null' we merge a comparison of a column
and 'column IS NULL' to one test. This is useful for sub select queries
that are internally transformed to something like:.
@code
SELECT * FROM t1 WHERE t1.key=outer_ref_field or t1.key IS NULL
@endcode
Key_field::null_rejecting is processed as follows: @n
result has null_rejecting=true if it is set for both ORed references.
for example:
- (t2.key = t1.field OR t2.key = t1.field) -> null_rejecting=true
- (t2.key = t1.field OR t2.key <=> t1.field) -> null_rejecting=false
@todo
The result of this is that we're missing some 'ref' accesses.
OptimizerTeam: Fix this
*/
static Key_field *
merge_key_fields(Key_field *start, Key_field *new_fields, Key_field *end,
uint and_level)
{
if (start == new_fields)
return start; // Impossible or
if (new_fields == end)
return start; // No new fields, skip all
Key_field *first_free=new_fields;
/* Mark all found fields in old array */
for (; new_fields != end ; new_fields++)
{
Field *const new_field= new_fields->item_field->field;
for (Key_field *old=start ; old != first_free ; old++)
{
Field *const old_field= old->item_field->field;
/*
Check that the Field objects are the same, as we may have several
Item_field objects pointing to the same Field:
*/
if (old_field == new_field)
{
/*
NOTE: below const_item() call really works as "!used_tables()", i.e.
it can return FALSE where it is feasible to make it return TRUE.
The cause is as follows: Some of the tables are already known to be
const tables (the detection code is in JOIN::make_join_plan(),
above the update_ref_and_keys() call), but we didn't propagate
information about this: TABLE::const_table is not set to TRUE, and
Item::update_used_tables() hasn't been called for each item.
The result of this is that we're missing some 'ref' accesses.
TODO: OptimizerTeam: Fix this
*/
if (!new_fields->val->const_item())
{
/*
If the value matches, we can use the key reference.
If not, we keep it until we have examined all new values
*/
if (old->val->eq(new_fields->val, old_field->binary()))
{
old->level= and_level;
old->optimize= ((old->optimize & new_fields->optimize &
KEY_OPTIMIZE_EXISTS) |
((old->optimize | new_fields->optimize) &
KEY_OPTIMIZE_REF_OR_NULL));
old->null_rejecting= (old->null_rejecting &&
new_fields->null_rejecting);
}
}
else if (old->eq_func && new_fields->eq_func &&
old->val->eq_by_collation(new_fields->val,
old_field->binary(),
old_field->charset()))
{
old->level= and_level;
old->optimize= ((old->optimize & new_fields->optimize &
KEY_OPTIMIZE_EXISTS) |
((old->optimize | new_fields->optimize) &
KEY_OPTIMIZE_REF_OR_NULL));
old->null_rejecting= (old->null_rejecting &&
new_fields->null_rejecting);
}
else if (old->eq_func && new_fields->eq_func &&
((old->val->const_item() && old->val->is_null()) ||
new_fields->val->is_null()))
{
/* field = expression OR field IS NULL */
old->level= and_level;
old->optimize= KEY_OPTIMIZE_REF_OR_NULL;
/*
Remember the NOT NULL value unless the value does not depend
on other tables.
*/
if (!old->val->used_tables() && old->val->is_null())
old->val= new_fields->val;
/* The referred expression can be NULL: */
old->null_rejecting= 0;
}
else
{
/*
We are comparing two different const. In this case we can't
use a key-lookup on this so it's better to remove the value
and let the range optimizer handle it
*/
if (old == --first_free) // If last item
break;
*old= *first_free; // Remove old value
old--; // Retry this value
}
}
}
}
/* Remove all not used items */
for (Key_field *old=start ; old != first_free ;)
{
if (old->level != and_level)
{ // Not used in all levels
if (old == --first_free)
break;
*old= *first_free; // Remove old value
continue;
}
old++;
}
return first_free;
}
/**
Given a field, return its index in semi-join's select list, or UINT_MAX
@param item_field Field to be looked up in select list
@retval =UINT_MAX Field is not from a semijoin-transformed subquery
@retval <UINT_MAX Index in select list of subquery
@details
Given a field, find its table; then see if the table is within a
semi-join nest and if the field was in select list of the subquery
(if subquery was part of a quantified comparison predicate), or
the field was a result of subquery decorrelation.
If it was, then return the field's index in the select list.
The value is used by LooseScan strategy.
*/
static uint get_semi_join_select_list_index(Item_field *item_field)
{
TABLE_LIST *emb_sj_nest= item_field->table_ref->embedding;
if (emb_sj_nest && emb_sj_nest->sj_cond())
{
List<Item> &items= emb_sj_nest->nested_join->sj_inner_exprs;
List_iterator<Item> it(items);
for (uint i= 0; i < items.elements; i++)
{
Item *sel_item= it++;
if (sel_item->type() == Item::FIELD_ITEM &&
((Item_field*)sel_item)->field->eq(item_field->field))
return i;
}
}
return UINT_MAX;
}
/**
@brief
If EXPLAIN EXTENDED or if the --safe-updates option is enabled, add a
warning that an index cannot be used for ref access
@details
If EXPLAIN EXTENDED or if the --safe-updates option is enabled, add a
warning for each index that cannot be used for ref access due to either type
conversion or different collations on the field used for comparison
Example type conversion (char compared to int):
CREATE TABLE t1 (url char(1) PRIMARY KEY);
SELECT * FROM t1 WHERE url=1;
Example different collations (danish vs german2):
CREATE TABLE t1 (url char(1) PRIMARY KEY) collate latin1_danish_ci;
SELECT * FROM t1 WHERE url='1' collate latin1_german2_ci;
@param thd Thread for the connection that submitted the query
@param field Field used in comparision
@param cant_use_index Indexes that cannot be used for lookup
*/
static void
warn_index_not_applicable(THD *thd, const Field *field,
const key_map cant_use_index)
{
if (thd->lex->describe ||
thd->variables.option_bits & OPTION_SAFE_UPDATES)
for (uint j=0 ; j < field->table->s->keys ; j++)
if (cant_use_index.is_set(j))
push_warning_printf(thd,
Sql_condition::SL_WARNING,
ER_WARN_INDEX_NOT_APPLICABLE,
ER(ER_WARN_INDEX_NOT_APPLICABLE),
"ref",
field->table->key_info[j].name,
field->field_name);
}
/**
Add a possible key to array of possible keys if it's usable as a key
@param key_fields[in,out] Used as an input paramater in the sense that it is a
pointer to a pointer to a memory area where an array of Key_field objects will
stored. It is used as an out parameter in the sense that the pointer will be
updated to point beyond the last Key_field written.
@param and_level And level, to be stored in Key_field
@param cond Condition predicate
@param field Field used in comparision
@param eq_func True if we used =, <=> or IS NULL
@param value Array of values used for comparison with field
@param num_values Number of elements in the array of values
@param usable_tables Tables which can be used for key optimization
@param sargables IN/OUT Array of found sargable candidates. Will be
ignored in case eq_func is true.
@note
If we are doing a NOT NULL comparison on a NOT NULL field in a outer join
table, we store this to be able to do not exists optimization later.
@return
*key_fields is incremented if we stored a key in the array
*/
static void
add_key_field(Key_field **key_fields, uint and_level, Item_func *cond,
Item_field *item_field, bool eq_func, Item **value,
uint num_values, table_map usable_tables,
SARGABLE_PARAM **sargables)
{
assert(eq_func || sargables);
Field *const field= item_field->field;
TABLE_LIST *const tl= item_field->table_ref;
if (tl->table->reginfo.join_tab == NULL)
{
/*
Due to a bug in IN-to-EXISTS (grep for real_item() in item_subselect.cc
for more info), an index over a field from an outer query might be
considered here, which is incorrect. Their query has been fully
optimized already so their reginfo.join_tab is NULL and we reject them.
*/
return;
}
DBUG_PRINT("info", ("add_key_field for field %s", field->field_name));
uint exists_optimize= 0;
if (!tl->derived_keys_ready && tl->uses_materialization() &&
!tl->table->is_created() &&
tl->update_derived_keys(field, value, num_values))
return;
if (!(field->flags & PART_KEY_FLAG))
{
// Don't remove column IS NULL on a LEFT JOIN table
if (!eq_func || (*value)->type() != Item::NULL_ITEM ||
!tl->table->is_nullable() || field->real_maybe_null())
return; // Not a key. Skip it
exists_optimize= KEY_OPTIMIZE_EXISTS;
assert(num_values == 1);
}
else
{
table_map used_tables= 0;
bool optimizable= false;
for (uint i=0; i<num_values; i++)
{
used_tables|=(value[i])->used_tables();
if (!((value[i])->used_tables() & (tl->map() | RAND_TABLE_BIT)))
optimizable= true;
}
if (!optimizable)
return;
if (!(usable_tables & tl->map()))
{
if (!eq_func || (*value)->type() != Item::NULL_ITEM ||
!tl->table->is_nullable() || field->real_maybe_null())
return; // Can't use left join optimize
exists_optimize= KEY_OPTIMIZE_EXISTS;
}
else
{
JOIN_TAB *stat= tl->table->reginfo.join_tab;
key_map possible_keys=field->key_start;
possible_keys.intersect(tl->table->keys_in_use_for_query);
stat[0].keys().merge(possible_keys); // Add possible keys
/*
Save the following cases:
Field op constant
Field LIKE constant where constant doesn't start with a wildcard
Field = field2 where field2 is in a different table
Field op formula
Field IS NULL
Field IS NOT NULL
Field BETWEEN ...
Field IN ...
*/
stat[0].key_dependent|=used_tables;
bool is_const= true;
for (uint i=0; i<num_values; i++)
{
if (!(is_const&= value[i]->const_item()))
break;
}
if (is_const)
stat[0].const_keys.merge(possible_keys);
else if (!eq_func)
{
/*
Save info to be able check whether this predicate can be
considered as sargable for range analysis after reading const tables.
We do not save info about equalities as update_const_equal_items
will take care of updating info on keys from sargable equalities.
*/
assert(sargables);
(*sargables)--;
/*
The sargables and key_fields arrays share the same memory
buffer, and grow from opposite directions, so make sure they
don't cross.
*/
assert(*sargables > *reinterpret_cast<SARGABLE_PARAM**>(key_fields));
(*sargables)->field= field;
(*sargables)->arg_value= value;
(*sargables)->num_values= num_values;
}
/*
We can't always use indexes when comparing a string index to a
number. cmp_type() is checked to allow compare of dates to numbers.
eq_func is NEVER true when num_values > 1
*/
if (!eq_func)
return;
/*
Check if the field and value are comparable in the index.
@todo: This code is almost identical to comparable_in_index()
in opt_range.cc. Consider replacing the checks below with a
function call to comparable_in_index()
*/
if (field->result_type() == STRING_RESULT)
{
if ((*value)->result_type() != STRING_RESULT)
{
if (field->cmp_type() != (*value)->result_type())
{
warn_index_not_applicable(stat->join()->thd, field, possible_keys);
return;
}
}
else
{
/*
Can't optimize datetime_column=indexed_varchar_column,
also can't use indexes if the effective collation
of the operation differ from the field collation.
IndexedTimeComparedToDate: can't optimize
'indexed_time = temporal_expr_with_date_part' because:
- without index, a TIME column with value '48:00:00' is equal to a
DATETIME column with value 'CURDATE() + 2 days'
- with ref access into the TIME column, CURDATE() + 2 days becomes
"00:00:00" (Field_timef::store_internal() simply extracts the time
part from the datetime) which is a lookup key which does not match
"48:00:00"; so ref access is not be able to give the same result
as without index, so is disabled.
On the other hand, we can optimize indexed_datetime = time
because Field_temporal_with_date::store_time() will convert
48:00:00 to CURDATE() + 2 days which is the correct lookup key.
*/
if ((!field->is_temporal() && value[0]->is_temporal()) ||
(field->cmp_type() == STRING_RESULT &&
field->charset() != cond->compare_collation()) ||
field_time_cmp_date(field, value[0]))
{
warn_index_not_applicable(stat->join()->thd, field, possible_keys);
return;
}
}
}
/*
We can't use indexes when comparing to a JSON value. For example,
the string '{}' should compare equal to the JSON string "{}". If
we use a string index to compare the two strings, we will be
comparing '{}' and '"{}"', which don't compare equal.
*/
if (value[0]->result_type() == STRING_RESULT &&
value[0]->field_type() == MYSQL_TYPE_JSON)
{
warn_index_not_applicable(stat->join()->thd, field, possible_keys);
return;
}
}
}
/*
For the moment eq_func is always true. This slot is reserved for future
extensions where we want to remembers other things than just eq comparisons
*/
assert(eq_func);
/*
If the condition has form "tbl.keypart = othertbl.field" and
othertbl.field can be NULL, there will be no matches if othertbl.field
has NULL value.
We use null_rejecting in add_not_null_conds() to add
'othertbl.field IS NOT NULL' to tab->m_condition, if this is not an outer
join. We also use it to shortcut reading "tbl" when othertbl.field is
found to be a NULL value (in join_read_always_key() and BKA).
*/
Item *const real= (*value)->real_item();
const bool null_rejecting=
((cond->functype() == Item_func::EQ_FUNC) ||
(cond->functype() == Item_func::MULT_EQUAL_FUNC)) &&
(real->type() == Item::FIELD_ITEM) &&
((Item_field*)real)->field->maybe_null();
/* Store possible eq field */
new (*key_fields)
Key_field(item_field, *value, and_level, exists_optimize, eq_func,
null_rejecting, NULL,
get_semi_join_select_list_index(item_field));
(*key_fields)++;
/*
The sargables and key_fields arrays share the same memory buffer,
and grow from opposite directions, so make sure they don't
cross. But if sargables was NULL, eq_func had to be true and we
don't write any sargables.
*/
assert(sargables == NULL ||
*key_fields < *reinterpret_cast<Key_field**>(sargables));
}
/**
Add possible keys to array of possible keys originated from a simple
predicate.
@param key_fields Pointer to add key, if usable
@param and_level And level, to be stored in Key_field
@param cond Condition predicate
@param field_item Field used in comparision
@param eq_func True if we used =, <=> or IS NULL
@param val Value used for comparison with field
Is NULL for BETWEEN and IN
@param usable_tables Tables which can be used for key optimization
@param sargables IN/OUT Array of found sargable candidates
@note
If field items f1 and f2 belong to the same multiple equality and
a key is added for f1, the the same key is added for f2.
@returns
*key_fields is incremented if we stored a key in the array
*/
static void
add_key_equal_fields(Key_field **key_fields, uint and_level,
Item_func *cond, Item_field *field_item,
bool eq_func, Item **val,
uint num_values, table_map usable_tables,
SARGABLE_PARAM **sargables)
{
DBUG_ENTER("add_key_equal_fields");
add_key_field(key_fields, and_level, cond, field_item,
eq_func, val, num_values, usable_tables, sargables);
Item_equal *item_equal= field_item->item_equal;
if (item_equal)
{
/*
Add to the set of possible key values every substitution of
the field for an equal field included into item_equal
*/
Item_equal_iterator it(*item_equal);
Item_field *item;
while ((item= it++))
{
if (!field_item->field->eq(item->field))
add_key_field(key_fields, and_level, cond, item,
eq_func, val, num_values, usable_tables,
sargables);
}
}
DBUG_VOID_RETURN;
}
/**
Check if an expression is a non-outer field.
Checks if an expression is a field and belongs to the current select.
@param field Item expression to check
@return boolean
@retval TRUE the expression is a local field
@retval FALSE it's something else
*/
static bool
is_local_field (Item *field)
{
return field->real_item()->type() == Item::FIELD_ITEM &&
!(field->used_tables() & OUTER_REF_TABLE_BIT) &&
!down_cast<Item_ident *>(field)->depended_from &&
!down_cast<Item_ident *>(field->real_item())->depended_from;
}
/**
Check if a row constructor expression is over columns in the same query block.
@param item_row Row expression to check.
@return boolean
@retval true The expression is a local column reference.
@retval false It's something else.
*/
static bool is_row_of_local_columns(Item_row *item_row)
{
for (uint i= 0; i < item_row->cols(); ++i)
if (!is_local_field(item_row->element_index(i)))
return false;
return true;
}
/**
The guts of the ref optimizer. This function, along with the other
add_key_* functions, make up a recursive procedure that analyzes a
condition expression (a tree of AND and OR predicates) and does
many things.
@param join The query block involving the condition.
@param key_fields[in,out] Start of memory buffer, see below.
@param and_level[in, out] Current 'and level', see below.
@param cond The conditional expression to analyze.
@param usable_tables Tables not in this bitmap will not be examined.
@param sargables [in,out] End of memory buffer, see below.
This documentation is the result of reverse engineering and may
therefore not capture the full gist of the procedure, but it is
known to do the following:
- Populate a raw memory buffer from two directions at the same time. An
'array' of Key_field objects fill the buffer from low to high addresses
whilst an 'array' of SARGABLE_PARAM's fills the buffer from high to low
addresses. At the first call to this function, it is assumed that
key_fields points to the beginning of the buffer and sargables point to the
end (except for a poor-mans 'null element' at the very end).
- Update a number of properties in the JOIN_TAB's that can be used
to find search keys (sargables).
- JOIN_TAB::keys
- JOIN_TAB::key_dependent
- JOIN_TAB::const_keys (dictates if the range optimizer will be run
later.)
The Key_field objects are marked with something called an 'and_level', which
does @b not correspond to their nesting depth within the expression tree. It
is rather a tag to group conjunctions together. For instance, in the
conditional expression
@code
a = 0 AND b = 0
@endcode
two Key_field's are produced, both having an and_level of 0.
In an expression such as
@code
a = 0 AND b = 0 OR a = 1
@endcode
three Key_field's are produced, the first two corresponding to 'a = 0' and
'b = 0', respectively, both with and_level 0. The third one corresponds to
'a = 1' and has an and_level of 1.
A separate function, merge_key_fields() performs ref access validation on
the Key_field array on the recursice ascent. If some Key_field's cannot be
used for ref access, the key_fields pointer is rolled back. All other
modifications to the query plan remain.
*/
static void
add_key_fields(JOIN *join, Key_field **key_fields, uint *and_level,
Item *cond, table_map usable_tables,
SARGABLE_PARAM **sargables)
{
DBUG_ENTER("add_key_fields");
if (cond->type() == Item_func::COND_ITEM)
{
List_iterator_fast<Item> li(*((Item_cond*) cond)->argument_list());
Key_field *org_key_fields= *key_fields;
if (((Item_cond*) cond)->functype() == Item_func::COND_AND_FUNC)
{
Item *item;
while ((item=li++))
add_key_fields(join, key_fields, and_level, item, usable_tables,
sargables);
for (; org_key_fields != *key_fields ; org_key_fields++)
org_key_fields->level= *and_level;
}
else
{
(*and_level)++;
add_key_fields(join, key_fields, and_level, li++, usable_tables,
sargables);
Item *item;
while ((item=li++))
{
Key_field *start_key_fields= *key_fields;
(*and_level)++;
add_key_fields(join, key_fields, and_level, item, usable_tables,
sargables);
*key_fields=merge_key_fields(org_key_fields,start_key_fields,
*key_fields,++(*and_level));
}
}
DBUG_VOID_RETURN;
}
/*
Subquery optimization: Conditions that are pushed down into subqueries
are wrapped into Item_func_trig_cond. We process the wrapped condition
but need to set cond_guard for Key_use elements generated from it.
*/
{
if (cond->type() == Item::FUNC_ITEM &&
((Item_func*)cond)->functype() == Item_func::TRIG_COND_FUNC)
{
Item *cond_arg= ((Item_func*)cond)->arguments()[0];
if (!join->group_list && !join->order &&
join->unit->item &&
join->unit->item->substype() == Item_subselect::IN_SUBS &&
!join->unit->is_union())
{
Key_field *save= *key_fields;
add_key_fields(join, key_fields, and_level, cond_arg, usable_tables,
sargables);
// Indicate that this ref access candidate is for subquery lookup:
for (; save != *key_fields; save++)
save->cond_guard= ((Item_func_trig_cond*)cond)->get_trig_var();
}
DBUG_VOID_RETURN;
}
}
/* If item is of type 'field op field/constant' add it to key_fields */
if (cond->type() != Item::FUNC_ITEM)
DBUG_VOID_RETURN;
Item_func *cond_func= (Item_func*) cond;
switch (cond_func->select_optimize()) {
case Item_func::OPTIMIZE_NONE:
break;
case Item_func::OPTIMIZE_KEY:
{
Item **values;
/*
Build list of possible keys for 'a BETWEEN low AND high'.
It is handled similar to the equivalent condition
'a >= low AND a <= high':
*/
if (cond_func->functype() == Item_func::BETWEEN)
{
Item_field *field_item;
bool equal_func= FALSE;
uint num_values= 2;
values= cond_func->arguments();
bool binary_cmp= (values[0]->real_item()->type() == Item::FIELD_ITEM)
? ((Item_field*)values[0]->real_item())->field->binary()
: TRUE;
/*
Additional optimization: If 'low = high':
Handle as if the condition was "t.key = low".
*/
if (!((Item_func_between*)cond_func)->negated &&
values[1]->eq(values[2], binary_cmp))
{
equal_func= TRUE;
num_values= 1;
}
/*
Append keys for 'field <cmp> value[]' if the
condition is of the form::
'<field> BETWEEN value[1] AND value[2]'
*/
if (is_local_field (values[0]))
{
field_item= (Item_field *) (values[0]->real_item());
add_key_equal_fields(key_fields, *and_level, cond_func,
field_item, equal_func, &values[1],
num_values, usable_tables, sargables);
}
/*
Append keys for 'value[0] <cmp> field' if the
condition is of the form:
'value[0] BETWEEN field1 AND field2'
*/
for (uint i= 1; i <= num_values; i++)
{
if (is_local_field (values[i]))
{
field_item= (Item_field *) (values[i]->real_item());
add_key_equal_fields(key_fields, *and_level, cond_func,
field_item, equal_func, values,
1, usable_tables, sargables);
}
}
} // if ( ... Item_func::BETWEEN)
// The predicate is IN or !=
else if (is_local_field (cond_func->key_item()) &&
!(cond_func->used_tables() & OUTER_REF_TABLE_BIT))
{
values= cond_func->arguments()+1;
if (cond_func->functype() == Item_func::NE_FUNC &&
is_local_field (cond_func->arguments()[1]))
values--;
assert(cond_func->functype() != Item_func::IN_FUNC ||
cond_func->argument_count() != 2);
add_key_equal_fields(key_fields, *and_level, cond_func,
(Item_field*) (cond_func->key_item()->real_item()),
0, values,
cond_func->argument_count()-1,
usable_tables, sargables);
}
else if (cond_func->functype() == Item_func::IN_FUNC &&
cond_func->key_item()->type() == Item::ROW_ITEM)
{
/*
The condition is (column1, column2, ... ) IN ((const1_1, const1_2), ...)
and there is an index on (column1, column2, ...)
The code below makes sure that the row constructor on the lhs indeed
contains only column references before calling add_key_field on them.
We can't do a ref access on IN, yet here we are. Why? We need
to run add_key_field() only because it verifies that there are
only constant expressions in the rows on the IN's rhs, see
comment above the call to add_key_field() below.
Actually, We could in theory do a ref access if the IN rhs
contained just a single row, but there is a hack in the parser
causing such IN predicates be parsed as row equalities.
*/
Item_row *lhs_row= static_cast<Item_row*>(cond_func->key_item());
if (is_row_of_local_columns(lhs_row))
{
for (uint i= 0; i < lhs_row->cols(); ++i)
{
Item *const lhs_item= lhs_row->element_index(i)->real_item();
assert(lhs_item->type() == Item::FIELD_ITEM);
Item_field *const lhs_column= static_cast<Item_field*>(lhs_item);
// j goes from 1 since arguments()[0] is the lhs of IN.
for (uint j= 1; j < cond_func->argument_count(); ++j)
{
// Here we pick out the i:th column in the j:th row.
Item *rhs_item= cond_func->arguments()[j];
assert(rhs_item->type() == Item::ROW_ITEM);
Item_row *rhs_row= static_cast<Item_row*>(rhs_item);
assert(rhs_row->cols() == lhs_row->cols());
Item **rhs_expr_ptr= rhs_row->addr(i);
/*
add_key_field() will write a Key_field on each call
here, but we don't care, it will never be used. We only
call it for the side effect: update JOIN_TAB::const_keys
so the range optimizer can be invoked. We pass a
scrap buffer and pointer here.
*/
Key_field scrap_key_field= **key_fields;
Key_field *scrap_key_field_ptr= &scrap_key_field;
add_key_field(&scrap_key_field_ptr,
*and_level,
cond_func,
lhs_column,
true, // eq_func
rhs_expr_ptr,
1, // Number of expressions: one
usable_tables,
NULL); // sargables
// The pointer is not supposed to increase by more than one.
assert(scrap_key_field_ptr <= &scrap_key_field + 1);
}
}
}
}
break;
}
case Item_func::OPTIMIZE_OP:
{
bool equal_func=(cond_func->functype() == Item_func::EQ_FUNC ||
cond_func->functype() == Item_func::EQUAL_FUNC);
if (is_local_field (cond_func->arguments()[0]))
{
add_key_equal_fields(key_fields, *and_level, cond_func,
(Item_field*) (cond_func->arguments()[0])->real_item(),
equal_func,
cond_func->arguments()+1, 1, usable_tables,
sargables);
}
if (is_local_field (cond_func->arguments()[1]) &&
cond_func->functype() != Item_func::LIKE_FUNC)
{
add_key_equal_fields(key_fields, *and_level, cond_func,
(Item_field*) (cond_func->arguments()[1])->real_item(),
equal_func,
cond_func->arguments(),1,usable_tables,
sargables);
}
break;
}
case Item_func::OPTIMIZE_NULL:
/* column_name IS [NOT] NULL */
if (is_local_field (cond_func->arguments()[0]) &&
!(cond_func->used_tables() & OUTER_REF_TABLE_BIT))
{
Item *tmp=new Item_null;
if (unlikely(!tmp)) // Should never be true
DBUG_VOID_RETURN;
add_key_equal_fields(key_fields, *and_level, cond_func,
(Item_field*) (cond_func->arguments()[0])->real_item(),
cond_func->functype() == Item_func::ISNULL_FUNC,
&tmp, 1, usable_tables, sargables);
}
break;
case Item_func::OPTIMIZE_EQUAL:
Item_equal *item_equal= (Item_equal *) cond;
Item *const_item= item_equal->get_const();
if (const_item)
{
/*
For each field field1 from item_equal consider the equality
field1=const_item as a condition allowing an index access of the table
with field1 by the keys value of field1.
*/
Item_equal_iterator it(*item_equal);
Item_field *item;
while ((item= it++))
{
add_key_field(key_fields, *and_level, cond_func, item,
TRUE, &const_item, 1, usable_tables, sargables);
}
}
else
{
/*
Consider all pairs of different fields included into item_equal.
For each of them (field1, field1) consider the equality
field1=field2 as a condition allowing an index access of the table
with field1 by the keys value of field2.
*/
Item_equal_iterator outer_it(*item_equal);
Item_equal_iterator inner_it(*item_equal);
Item_field *outer;
while ((outer= outer_it++))
{
Item_field *inner;
while ((inner= inner_it++))
{
if (!outer->field->eq(inner->field))
add_key_field(key_fields, *and_level, cond_func, outer,
true, (Item **) &inner, 1, usable_tables,
sargables);
}
inner_it.rewind();
}
}
break;
}
DBUG_VOID_RETURN;
}
/*
Add all keys with uses 'field' for some keypart
If field->and_level != and_level then only mark key_part as const_part
RETURN
0 - OK
1 - Out of memory.
*/
static bool
add_key_part(Key_use_array *keyuse_array, Key_field *key_field)
{
if (key_field->eq_func && !(key_field->optimize & KEY_OPTIMIZE_EXISTS))
{
Field *const field= key_field->item_field->field;
TABLE_LIST *const tl= key_field->item_field->table_ref;
TABLE *const table= tl->table;
for (uint key=0 ; key < table->s->keys ; key++)
{
if (!(table->keys_in_use_for_query.is_set(key)))
continue;
if (table->key_info[key].flags & (HA_FULLTEXT | HA_SPATIAL))
continue; // ToDo: ft-keys in non-ft queries. SerG
uint key_parts= actual_key_parts(&table->key_info[key]);
for (uint part=0 ; part < key_parts ; part++)
{
if (field->eq(table->key_info[key].key_part[part].field))
{
const Key_use keyuse(tl,
key_field->val,
key_field->val->used_tables(),
key,
part,
key_field->optimize & KEY_OPTIMIZE_REF_OR_NULL,
(key_part_map) 1 << part,
~(ha_rows) 0, // will be set in optimize_keyuse
key_field->null_rejecting,
key_field->cond_guard,
key_field->sj_pred_no);
if (keyuse_array->push_back(keyuse))
return true; /* purecov: inspected */
}
}
}
}
return false;
}
/**
Function parses WHERE condition and add key_use for FT index
into key_use array if suitable MATCH function is found.
Condition should be a set of AND expression, OR is not supported.
MATCH function should be a part of simple expression.
Simple expression is MATCH only function or MATCH is a part of
comparison expression ('>=' or '>' operations are supported).
It also sets FT_HINTS values(op_type, op_value).
@param keyuse_array Key_use array
@param stat JOIN_TAB structure
@param cond WHERE condition
@param usable_tables usable tables
@param simple_match_expr true if this is the first call false otherwise.
if MATCH function is found at first call it means
that MATCH is simple expression, otherwise, in case
of AND/OR condition this parameter will be false.
@retval
true if FT key was added to Key_use array
@retval
false if no key was added to Key_use array
*/
static bool
add_ft_keys(Key_use_array *keyuse_array,
JOIN_TAB *stat,Item *cond,table_map usable_tables,
bool simple_match_expr)
{
Item_func_match *cond_func=NULL;
if (!cond)
return FALSE;
if (cond->type() == Item::FUNC_ITEM)
{
Item_func *func=(Item_func *)cond;
Item_func::Functype functype= func->functype();
enum ft_operation op_type= FT_OP_NO;
double op_value= 0.0;
if (functype == Item_func::FT_FUNC)
{
cond_func= ((Item_func_match *) cond)->get_master();
cond_func->set_hints_op(op_type, op_value);
}
else if (func->arg_count == 2)
{
Item *arg0=(func->arguments()[0]),
*arg1=(func->arguments()[1]);
if (arg1->const_item() &&
arg0->type() == Item::FUNC_ITEM &&
((Item_func *) arg0)->functype() == Item_func::FT_FUNC &&
((functype == Item_func::GE_FUNC &&
(op_value= arg1->val_real()) > 0) ||
(functype == Item_func::GT_FUNC &&
(op_value= arg1->val_real()) >=0)))
{
cond_func= ((Item_func_match *) arg0)->get_master();
if (functype == Item_func::GE_FUNC)
op_type= FT_OP_GE;
else if (functype == Item_func::GT_FUNC)
op_type= FT_OP_GT;
cond_func->set_hints_op(op_type, op_value);
}
else if (arg0->const_item() &&
arg1->type() == Item::FUNC_ITEM &&
((Item_func *) arg1)->functype() == Item_func::FT_FUNC &&
((functype == Item_func::LE_FUNC &&
(op_value= arg0->val_real()) > 0) ||
(functype == Item_func::LT_FUNC &&
(op_value= arg0->val_real()) >=0)))
{
cond_func= ((Item_func_match *) arg1)->get_master();
if (functype == Item_func::LE_FUNC)
op_type= FT_OP_GE;
else if (functype == Item_func::LT_FUNC)
op_type= FT_OP_GT;
cond_func->set_hints_op(op_type, op_value);
}
}
}
else if (cond->type() == Item::COND_ITEM)
{
List_iterator_fast<Item> li(*((Item_cond*) cond)->argument_list());
if (((Item_cond*) cond)->functype() == Item_func::COND_AND_FUNC)
{
Item *item;
while ((item=li++))
{
if (add_ft_keys(keyuse_array, stat, item, usable_tables, false))
return TRUE;
}
}
}
if (!cond_func || cond_func->key == NO_SUCH_KEY ||
!(usable_tables & cond_func->table_ref->map()))
return FALSE;
cond_func->set_simple_expression(simple_match_expr);
const Key_use keyuse(cond_func->table_ref,
cond_func,
cond_func->key_item()->used_tables(),
cond_func->key,
FT_KEYPART,
0, // optimize
0, // keypart_map
~(ha_rows)0, // ref_table_rows
false, // null_rejecting
NULL, // cond_guard
UINT_MAX); // sj_pred_no
return keyuse_array->push_back(keyuse);
}
/**
Compares two keyuse elements.
@param a first Key_use element
@param b second Key_use element
Compare Key_use elements so that they are sorted as follows:
-# By table.
-# By key for each table.
-# By keypart for each key.
-# Const values.
-# Ref_or_null.
@retval 0 If a = b.
@retval <0 If a < b.
@retval >0 If a > b.
*/
static int sort_keyuse(Key_use *a, Key_use *b)
{
int res;
if (a->table_ref->tableno() != b->table_ref->tableno())
return (int) (a->table_ref->tableno() - b->table_ref->tableno());
if (a->key != b->key)
return (int) (a->key - b->key);
if (a->keypart != b->keypart)
return (int) (a->keypart - b->keypart);
// Place const values before other ones
if ((res= MY_TEST((a->used_tables & ~OUTER_REF_TABLE_BIT)) -
MY_TEST((b->used_tables & ~OUTER_REF_TABLE_BIT))))
return res;
/* Place rows that are not 'OPTIMIZE_REF_OR_NULL' first */
return (int) ((a->optimize & KEY_OPTIMIZE_REF_OR_NULL) -
(b->optimize & KEY_OPTIMIZE_REF_OR_NULL));
}
/*
Add to Key_field array all 'ref' access candidates within nested join.
This function populates Key_field array with entries generated from the
ON condition of the given nested join, and does the same for nested joins
contained within this nested join.
@param[in] nested_join_table Nested join pseudo-table to process
@param[in,out] end End of the key field array
@param[in,out] and_level And-level
@param[in,out] sargables Array of found sargable candidates
@note
We can add accesses to the tables that are direct children of this nested
join (1), and are not inner tables w.r.t their neighbours (2).
Example for #1 (outer brackets pair denotes nested join this function is
invoked for):
@code
... LEFT JOIN (t1 LEFT JOIN (t2 ... ) ) ON cond
@endcode
Example for #2:
@code
... LEFT JOIN (t1 LEFT JOIN t2 ) ON cond
@endcode
In examples 1-2 for condition cond, we can add 'ref' access candidates to
t1 only.
Example #3:
@code
... LEFT JOIN (t1, t2 LEFT JOIN t3 ON inner_cond) ON cond
@endcode
Here we can add 'ref' access candidates for t1 and t2, but not for t3.
*/
static void add_key_fields_for_nj(JOIN *join, TABLE_LIST *nested_join_table,
Key_field **end, uint *and_level,
SARGABLE_PARAM **sargables)
{
List_iterator<TABLE_LIST> li(nested_join_table->nested_join->join_list);
List_iterator<TABLE_LIST> li2(nested_join_table->nested_join->join_list);
bool have_another = FALSE;
table_map tables= 0;
TABLE_LIST *table;
assert(nested_join_table->nested_join);
while ((table= li++) || (have_another && (li=li2, have_another=FALSE,
(table= li++))))
{
if (table->nested_join)
{
if (!table->join_cond_optim())
{
/* It's a semi-join nest. Walk into it as if it wasn't a nest */
have_another= TRUE;
li2= li;
li= List_iterator<TABLE_LIST>(table->nested_join->join_list);
}
else
add_key_fields_for_nj(join, table, end, and_level, sargables);
}
else
if (!table->join_cond_optim())
tables|= table->map();
}
if (nested_join_table->join_cond_optim())
add_key_fields(join, end, and_level, nested_join_table->join_cond_optim(),
tables, sargables);
}
/// @} (end of group RefOptimizerModule)
/**
Check for the presence of AGGFN(DISTINCT a) queries that may be subject
to loose index scan.
Check if the query is a subject to AGGFN(DISTINCT) using loose index scan
(QUICK_GROUP_MIN_MAX_SELECT).
Optionally (if out_args is supplied) will push the arguments of
AGGFN(DISTINCT) to the list
Check for every COUNT(DISTINCT), AVG(DISTINCT) or
SUM(DISTINCT). These can be resolved by Loose Index Scan as long
as all the aggregate distinct functions refer to the same
fields. Thus:
SELECT AGGFN(DISTINCT a, b), AGGFN(DISTINCT b, a)... => can use LIS
SELECT AGGFN(DISTINCT a), AGGFN(DISTINCT a) ... => can use LIS
SELECT AGGFN(DISTINCT a, b), AGGFN(DISTINCT a) ... => cannot use LIS
SELECT AGGFN(DISTINCT a), AGGFN(DISTINCT b) ... => cannot use LIS
etc.
@param join the join to check
@param[out] out_args Collect the arguments of the aggregate functions
to a list. We don't worry about duplicates as
these will be sorted out later in
get_best_group_min_max.
@return does the query qualify for indexed AGGFN(DISTINCT)
@retval true it does
@retval false AGGFN(DISTINCT) must apply distinct in it.
*/
bool
is_indexed_agg_distinct(JOIN *join, List<Item_field> *out_args)
{
Item_sum **sum_item_ptr;
bool result= false;
Field_map first_aggdistinct_fields;
if (join->primary_tables > 1 || /* reference more than 1 table */
join->select_distinct || /* or a DISTINCT */
join->select_lex->olap == ROLLUP_TYPE) /* Check (B3) for ROLLUP */
return false;
if (join->make_sum_func_list(join->all_fields, join->fields_list, true))
return false;
for (sum_item_ptr= join->sum_funcs; *sum_item_ptr; sum_item_ptr++)
{
Item_sum *sum_item= *sum_item_ptr;
Field_map cur_aggdistinct_fields;
Item *expr;
/* aggregate is not AGGFN(DISTINCT) or more than 1 argument to it */
switch (sum_item->sum_func())
{
case Item_sum::MIN_FUNC:
case Item_sum::MAX_FUNC:
continue;
case Item_sum::COUNT_DISTINCT_FUNC:
break;
case Item_sum::AVG_DISTINCT_FUNC:
case Item_sum::SUM_DISTINCT_FUNC:
if (sum_item->get_arg_count() == 1)
break;
/* fall through */
default: return false;
}
for (uint i= 0; i < sum_item->get_arg_count(); i++)
{
expr= sum_item->get_arg(i);
/* The AGGFN(DISTINCT) arg is not an attribute? */
if (expr->real_item()->type() != Item::FIELD_ITEM)
return false;
Item_field* item= static_cast<Item_field*>(expr->real_item());
if (out_args)
out_args->push_back(item);
cur_aggdistinct_fields.set_bit(item->field->field_index);
result= true;
}
/*
If there are multiple aggregate functions, make sure that they all
refer to exactly the same set of columns.
*/
if (first_aggdistinct_fields.is_clear_all())
first_aggdistinct_fields.merge(cur_aggdistinct_fields);
else if (first_aggdistinct_fields != cur_aggdistinct_fields)
return false;
}
return result;
}
/**
Print keys that were appended to join_tab->const_keys because they
can be used for GROUP BY or DISTINCT to the optimizer trace.
@param trace The optimizer trace context we're adding info to
@param join_tab The table the indexes cover
@param new_keys The keys that are considered useful because they can
be used for GROUP BY or DISTINCT
@param cause Zero-terminated string with reason for adding indexes
to const_keys
@see add_group_and_distinct_keys()
*/
static void trace_indexes_added_group_distinct(Opt_trace_context *trace,
const JOIN_TAB *join_tab,
const key_map new_keys,
const char* cause)
{
#ifdef OPTIMIZER_TRACE
if (likely(!trace->is_started()))
return;
KEY *key_info= join_tab->table()->key_info;
key_map existing_keys= join_tab->const_keys;
uint nbrkeys= join_tab->table()->s->keys;
Opt_trace_object trace_summary(trace, "const_keys_added");
{
Opt_trace_array trace_key(trace,"keys");
for (uint j= 0 ; j < nbrkeys ; j++)
if (new_keys.is_set(j) && !existing_keys.is_set(j))
trace_key.add_utf8(key_info[j].name);
}
trace_summary.add_alnum("cause", cause);
#endif
}
/**
Discover the indexes that might be used for GROUP BY or DISTINCT queries.
If the query has a GROUP BY clause, find all indexes that contain
all GROUP BY fields, and add those indexes to join_tab->const_keys
and join_tab->keys.
If the query has a DISTINCT clause, find all indexes that contain
all SELECT fields, and add those indexes to join_tab->const_keys and
join_tab->keys. This allows later on such queries to be processed by
a QUICK_GROUP_MIN_MAX_SELECT.
Note that indexes that are not usable for resolving GROUP
BY/DISTINCT may also be added in some corner cases. For example, an
index covering 'a' and 'b' is not usable for the following query but
is still added: "SELECT DISTINCT a+b FROM t1". This is not a big
issue because a) although the optimizer will consider using the
index, it will not chose it (so minor calculation cost added but not
wrong result) and b) it applies only to corner cases.
@param join
@param join_tab
@return
None
*/
static void
add_group_and_distinct_keys(JOIN *join, JOIN_TAB *join_tab)
{
assert(join_tab->const_keys.is_subset(join_tab->keys()));
List<Item_field> indexed_fields;
List_iterator<Item_field> indexed_fields_it(indexed_fields);
ORDER *cur_group;
Item_field *cur_item;
const char *cause;
if (join->group_list)
{ /* Collect all query fields referenced in the GROUP clause. */
for (cur_group= join->group_list; cur_group; cur_group= cur_group->next)
(*cur_group->item)->walk(&Item::collect_item_field_processor,
Item::WALK_POSTFIX,
(uchar*) &indexed_fields);
cause= "group_by";
}
else if (join->select_distinct)
{ /* Collect all query fields referenced in the SELECT clause. */
List<Item> &select_items= join->fields_list;
List_iterator<Item> select_items_it(select_items);
Item *item;
while ((item= select_items_it++))
item->walk(&Item::collect_item_field_processor,
Item::WALK_POSTFIX,
(uchar*) &indexed_fields);
cause= "distinct";
}
else if (join->tmp_table_param.sum_func_count &&
is_indexed_agg_distinct(join, &indexed_fields))
{
/*
SELECT list with AGGFN(distinct col). The query qualifies for
loose index scan, and is_indexed_agg_distinct() has already
collected all referenced fields into indexed_fields.
*/
join->sort_and_group= 1;
cause= "indexed_distinct_aggregate";
}
else
return;
if (indexed_fields.elements == 0)
return;
key_map possible_keys;
possible_keys.set_all();
/* Intersect the keys of all group fields. */
while ((cur_item= indexed_fields_it++))
{
if (cur_item->used_tables() != join_tab->table_ref->map())
{
/*
Doing GROUP BY or DISTINCT on a field in another table so no
index in this table is usable
*/
return;
}
else
possible_keys.intersect(cur_item->field->part_of_key);
}
/*
At this point, possible_keys has key bits set only for usable
indexes because indexed_fields is non-empty and if any of the
fields belong to a different table the function would exit in the
loop above.
*/
if (!possible_keys.is_clear_all() &&
!possible_keys.is_subset(join_tab->const_keys))
{
trace_indexes_added_group_distinct(&join->thd->opt_trace, join_tab,
possible_keys, cause);
join_tab->const_keys.merge(possible_keys);
join_tab->keys().merge(possible_keys);
}
assert(join_tab->const_keys.is_subset(join_tab->keys()));
}
/**
Update keyuse array with all possible keys we can use to fetch rows.
@param thd
@param[out] keyuse Put here ordered array of Key_use structures
@param join_tab Array in table number order
@param tables Number of tables in join
@param cond WHERE condition (note that the function analyzes
join_tab[i]->join_cond() too)
@param normal_tables Tables not inner w.r.t some outer join (ones
for which we can make ref access based the WHERE
clause)
@param select_lex current SELECT
@param[out] sargables Array of found sargable candidates
@retval
0 OK
@retval
1 Out of memory.
*/
static bool
update_ref_and_keys(THD *thd, Key_use_array *keyuse,JOIN_TAB *join_tab,
uint tables, Item *cond, COND_EQUAL *cond_equal,
table_map normal_tables, SELECT_LEX *select_lex,
SARGABLE_PARAM **sargables)
{
uint and_level,i,found_eq_constant;
Key_field *key_fields, *end, *field;
size_t sz;
uint m= max(select_lex->max_equal_elems, 1U);
JOIN *const join= select_lex->join;
/*
We use the same piece of memory to store both Key_field
and SARGABLE_PARAM structure.
Key_field values are placed at the beginning this memory
while SARGABLE_PARAM values are put at the end.
All predicates that are used to fill arrays of Key_field
and SARGABLE_PARAM structures have at most 2 arguments
except BETWEEN predicates that have 3 arguments and
IN predicates.
This any predicate if it's not BETWEEN/IN can be used
directly to fill at most 2 array elements, either of Key_field
or SARGABLE_PARAM type. For a BETWEEN predicate 3 elements
can be filled as this predicate is considered as
saragable with respect to each of its argument.
An IN predicate can require at most 1 element as currently
it is considered as sargable only for its first argument.
Multiple equality can add elements that are filled after
substitution of field arguments by equal fields. There
can be not more than select_lex->max_equal_elems such
substitutions.
*/
sz= max(sizeof(Key_field), sizeof(SARGABLE_PARAM)) *
(((select_lex->cond_count + 1) * 2 +
select_lex->between_count) * m + 1);
if (!(key_fields=(Key_field*) thd->alloc(sz)))
return TRUE; /* purecov: inspected */
and_level= 0;
field= end= key_fields;
*sargables= (SARGABLE_PARAM *) key_fields +
(sz - sizeof((*sargables)[0].field))/sizeof(SARGABLE_PARAM);
/* set a barrier for the array of SARGABLE_PARAM */
(*sargables)[0].field= 0;
if (cond)
{
add_key_fields(join, &end, &and_level, cond, normal_tables, sargables);
for (Key_field *fld= field; fld != end ; fld++)
{
/* Mark that we can optimize LEFT JOIN */
if (fld->val->type() == Item::NULL_ITEM &&
!fld->item_field->field->real_maybe_null())
{
/*
Example:
SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.a WHERE t2.a IS NULL;
this just wants rows of t1 where t1.a does not exist in t2.
*/
fld->item_field->field->table->reginfo.not_exists_optimize= true;
}
}
}
for (i=0 ; i < tables ; i++)
{
/*
Block the creation of keys for inner tables of outer joins.
Here only the outer joins that can not be converted to
inner joins are left and all nests that can be eliminated
are flattened.
In the future when we introduce conditional accesses
for inner tables in outer joins these keys will be taken
into account as well.
*/
if (join_tab[i].join_cond())
add_key_fields(join, &end, &and_level,
join_tab[i].join_cond(),
join_tab[i].table_ref->map(), sargables);
}
/* Process ON conditions for the nested joins */
{
List_iterator<TABLE_LIST> li(select_lex->top_join_list);
TABLE_LIST *tl;
while ((tl= li++))
{
if (tl->nested_join)
add_key_fields_for_nj(join, tl, &end, &and_level, sargables);
}
}
/* Generate keys descriptions for derived tables */
if (select_lex->materialized_derived_table_count)
{
if (join->generate_derived_keys())
return true;
}
/* fill keyuse with found key parts */
for ( ; field != end ; field++)
{
if (add_key_part(keyuse,field))
return true;
}
if (select_lex->ftfunc_list->elements)
{
if (add_ft_keys(keyuse, join_tab, cond, normal_tables, true))
return true;
}
/*
Sort the array of possible keys and remove the following key parts:
- ref if there is a keypart which is a ref and a const.
(e.g. if there is a key(a,b) and the clause is a=3 and b=7 and b=t2.d,
then we skip the key part corresponding to b=t2.d)
- keyparts without previous keyparts
(e.g. if there is a key(a,b,c) but only b < 5 (or a=2 and c < 3) is
used in the query, we drop the partial key parts from consideration).
Special treatment for ft-keys.
*/
if (!keyuse->empty())
{
Key_use *save_pos, *use;
my_qsort(keyuse->begin(), keyuse->size(), keyuse->element_size(),
reinterpret_cast<qsort_cmp>(sort_keyuse));
const Key_use key_end(NULL, NULL, 0, 0, 0, 0, 0, 0, false, NULL, 0);
if (keyuse->push_back(key_end)) // added for easy testing
return TRUE;
use= save_pos= keyuse->begin();
const Key_use *prev= &key_end;
found_eq_constant=0;
for (i=0 ; i < keyuse->size()-1 ; i++,use++)
{
TABLE *const table= use->table_ref->table;
if (!use->used_tables && use->optimize != KEY_OPTIMIZE_REF_OR_NULL)
table->const_key_parts[use->key]|= use->keypart_map;
if (use->keypart != FT_KEYPART)
{
if (use->key == prev->key && use->table_ref == prev->table_ref)
{
if (prev->keypart+1 < use->keypart ||
(prev->keypart == use->keypart && found_eq_constant))
continue; /* remove */
}
else if (use->keypart != 0) // First found must be 0
continue;
}
#if defined(__GNUC__) && !MY_GNUC_PREREQ(4,4)
/*
Old gcc used a memcpy(), which is undefined if save_pos==use:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19410
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39480
*/
if (save_pos != use)
#endif
*save_pos= *use;
prev=use;
found_eq_constant= !use->used_tables;
/* Save ptr to first use */
if (!table->reginfo.join_tab->keyuse())
table->reginfo.join_tab->set_keyuse(save_pos);
table->reginfo.join_tab->checked_keys.set_bit(use->key);
save_pos++;
}
i= (uint) (save_pos - keyuse->begin());
keyuse->at(i) = key_end;
keyuse->chop(i);
}
print_keyuse_array(&thd->opt_trace, keyuse);
return false;
}
/**
Create a keyuse array for a table with a primary key.
To be used when creating a materialized temporary table.
@param thd THD pointer, for memory allocation
@param table Table object representing table
@param keyparts Number of key parts in the primary key
@param outer_exprs List of items used for key lookup
@return Pointer to created keyuse array, or NULL if error
*/
Key_use_array *create_keyuse_for_table(THD *thd, TABLE *table, uint keyparts,
Item_field **fields,
List<Item> outer_exprs)
{
void *mem= thd->alloc(sizeof(Key_use_array));
if (!mem)
return NULL;
Key_use_array *keyuses= new (mem) Key_use_array(thd->mem_root);
List_iterator<Item> outer_expr(outer_exprs);
for (uint keypartno= 0; keypartno < keyparts; keypartno++)
{
Item *const item= outer_expr++;
Key_field key_field(fields[keypartno], item, 0, 0, true,
// null_rejecting must be true for field items only,
// add_not_null_conds() is incapable of handling
// other item types.
(item->type() == Item::FIELD_ITEM),
NULL, UINT_MAX);
if (add_key_part(keyuses, &key_field))
return NULL;
}
const Key_use key_end(NULL, NULL, 0, 0, 0, 0, 0, 0, false, NULL, 0);
if (keyuses->push_back(key_end)) // added for easy testing
return NULL;
return keyuses;
}
/**
Move const tables first in the position array.
Increment the number of const tables and set same basic properties for the
const table.
A const table looked up by a key has type JT_CONST.
A const table with a single row has type JT_SYSTEM.
@param tab Table that is designated as a const table
@param key The key definition to use for this table (NULL if table scan)
*/
void JOIN::mark_const_table(JOIN_TAB *tab, Key_use *key)
{
POSITION *const position= positions + const_tables;
position->table= tab;
position->key= key;
position->rows_fetched= 1.0; // This is a const table
position->filter_effect= 1.0;
position->prefix_rowcount= 1.0;
position->read_cost= 0.0;
position->ref_depend_map= 0;
position->loosescan_key= MAX_KEY; // Not a LooseScan
position->sj_strategy= SJ_OPT_NONE;
positions->use_join_buffer= false;
// Move the const table as far down as possible in best_ref
JOIN_TAB **pos= best_ref + const_tables + 1;
for (JOIN_TAB *next= best_ref[const_tables]; next != tab; pos++)
{
JOIN_TAB *const tmp= pos[0];
pos[0]= next;
next= tmp;
}
best_ref[const_tables]= tab;
tab->set_type(key ? JT_CONST : JT_SYSTEM);
const_table_map|= tab->table_ref->map();
const_tables++;
}
void JOIN::make_outerjoin_info()
{
DBUG_ENTER("JOIN::make_outerjoin_info");
assert(select_lex->outer_join);
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
select_lex->reset_nj_counters();
for (uint i= const_tables; i < tables; ++i)
{
JOIN_TAB *const tab= best_ref[i];
TABLE *const table= tab->table();
if (!table)
continue;
TABLE_LIST *const tbl= tab->table_ref;
if (tbl->outer_join)
{
/*
Table tab is the only one inner table for outer join.
(Like table t4 for the table reference t3 LEFT JOIN t4 ON t3.a=t4.a
is in the query above.)
*/
tab->set_last_inner(i);
tab->set_first_inner(i);
tab->init_join_cond_ref(tbl);
tab->cond_equal= tbl->cond_equal;
/*
If this outer join nest is embedded in another join nest,
link the join-tabs:
*/
TABLE_LIST *const outer_join_nest= tbl->outer_join_nest();
if (outer_join_nest)
tab->set_first_upper(outer_join_nest->nested_join->first_nested);
}
for (TABLE_LIST *embedding= tbl->embedding;
embedding;
embedding= embedding->embedding)
{
// Ignore join nests that are not outer join nests:
if (!embedding->join_cond_optim())
continue;
NESTED_JOIN *const nested_join= embedding->nested_join;
if (!nested_join->nj_counter)
{
/*
Table tab is the first inner table for nested_join.
Save reference to it in the nested join structure.
*/
nested_join->first_nested= i;
tab->init_join_cond_ref(embedding);
tab->cond_equal= tbl->cond_equal;
TABLE_LIST *const outer_join_nest= embedding->outer_join_nest();
if (outer_join_nest)
tab->set_first_upper(outer_join_nest->nested_join->first_nested);
}
if (tab->first_inner() == NO_PLAN_IDX)
tab->set_first_inner(nested_join->first_nested);
if (++nested_join->nj_counter < nested_join->nj_total)
break;
// Table tab is the last inner table for nested join.
best_ref[nested_join->first_nested]->set_last_inner(i);
}
}
DBUG_VOID_RETURN;
}
/**
Build a condition guarded by match variables for embedded outer joins.
When generating a condition for a table as part of an outer join condition
or the WHERE condition, the table in question may also be part of an
embedded outer join. In such cases, the condition must be guarded by
the match variable for this embedded outer join. Such embedded outer joins
may also be recursively embedded in other joins.
The function recursively adds guards for a condition ascending from tab
to root_tab, which is the first inner table of an outer join,
or NULL if the condition being handled is the WHERE clause.
@param idx index of the first inner table for the inner-most outer join
@param cond the predicate to be guarded (must be set)
@param root_idx index of the inner table to stop at
(is NO_PLAN_IDX if this is the WHERE clause)
@return
- pointer to the guarded predicate, if success
- NULL if error
*/
static Item*
add_found_match_trig_cond(JOIN *join, plan_idx idx, Item *cond,
plan_idx root_idx)
{
ASSERT_BEST_REF_IN_JOIN_ORDER(join);
assert(cond);
for ( ; idx != root_idx; idx= join->best_ref[idx]->first_upper())
{
if (!(cond= new Item_func_trig_cond(cond, NULL, join, idx,
Item_func_trig_cond::FOUND_MATCH)))
return NULL;
cond->quick_fix_field();
cond->update_used_tables();
}
return cond;
}
/**
Attach outer join conditions to generated table conditions in an optimal way.
@param last_tab - Last table that has been added to the current plan.
Pre-condition: If this is the last inner table of an outer
join operation, a join condition is attached to the first
inner table of that outer join operation.
@return false if success, true if error.
Outer join conditions are attached to individual tables, but we can analyze
those conditions only when reaching the last inner table of an outer join
operation. Notice also that a table can be last within several outer join
nests, hence the outer for() loop of this function.
Example:
SELECT * FROM t1 LEFT JOIN (t2 LEFT JOIN t3 ON t2.a=t3.a) ON t1.a=t2.a
Table t3 is last both in the join nest (t2 - t3) and in (t1 - (t2 - t3))
Thus, join conditions for both join nests will be evaluated when reaching
this table.
For each outer join operation processed, the join condition is split
optimally over the inner tables of the outer join. The split-out conditions
are later referred to as table conditions (but note that several table
conditions stemming from different join operations may be combined into
a composite table condition).
Example:
Consider the above query once more.
The predicate t1.a=t2.a can be evaluated when rows from t1 and t2 are ready,
ie at table t2. The predicate t2.a=t3.a can be evaluated at table t3.
Each non-constant split-out table condition is guarded by a match variable
that enables it only when a matching row is found for all the embedded
outer join operations.
Each split-out table condition is guarded by a variable that turns the
condition off just before a null-complemented row for the outer join
operation is formed. Thus, the join condition will not be checked for
the null-complemented row.
*/
bool JOIN::attach_join_conditions(plan_idx last_tab)
{
DBUG_ENTER("JOIN::attach_join_conditions");
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
for (plan_idx first_inner= best_ref[last_tab]->first_inner();
first_inner != NO_PLAN_IDX &&
best_ref[first_inner]->last_inner() == last_tab;
first_inner= best_ref[first_inner]->first_upper())
{
/*
Table last_tab is the last inner table of an outer join, locate
the corresponding join condition from the first inner table of the
same outer join:
*/
Item *const join_cond= best_ref[first_inner]->join_cond();
assert(join_cond);
/*
Add the constant part of the join condition to the first inner table
of the outer join.
*/
Item *cond= make_cond_for_table(join_cond, const_table_map,
(table_map) 0, false);
if (cond)
{
cond= new Item_func_trig_cond(cond, NULL, this, first_inner,
Item_func_trig_cond::IS_NOT_NULL_COMPL);
if (!cond)
DBUG_RETURN(true);
if (cond->fix_fields(thd, NULL))
DBUG_RETURN(true);
if (best_ref[first_inner]->and_with_condition(cond))
DBUG_RETURN(true);
}
/*
Split the non-constant part of the join condition into parts that
can be attached to the inner tables of the outer join.
*/
for (plan_idx i= first_inner; i <= last_tab; ++i)
{
table_map prefix_tables= best_ref[i]->prefix_tables();
table_map added_tables= best_ref[i]->added_tables();
/*
When handling the first inner table of an outer join, we may also
reference all tables ahead of this table:
*/
if (i == first_inner)
added_tables= prefix_tables;
/*
We need RAND_TABLE_BIT on the last inner table, in case there is a
non-deterministic function in the join condition.
(RAND_TABLE_BIT is set for the last table of the join plan,
but this is not sufficient for join conditions, which may have a
last inner table that is ahead of the last table of the join plan).
*/
if (i == last_tab)
{
prefix_tables|= RAND_TABLE_BIT;
added_tables|= RAND_TABLE_BIT;
}
cond= make_cond_for_table(join_cond, prefix_tables, added_tables, false);
if (cond == NULL)
continue;
/*
If the table is part of an outer join that is embedded in the
outer join currently being processed, wrap the condition in
triggered conditions for match variables of such embedded outer joins.
*/
if (!(cond= add_found_match_trig_cond(this, best_ref[i]->first_inner(),
cond, first_inner)))
DBUG_RETURN(true);
// Add the guard turning the predicate off for the null-complemented row.
cond= new Item_func_trig_cond(cond, NULL, this, first_inner,
Item_func_trig_cond::IS_NOT_NULL_COMPL);
if (!cond)
DBUG_RETURN(true);
if (cond->fix_fields(thd, NULL))
DBUG_RETURN(true);
// Add the generated condition to the existing table condition
if (best_ref[i]->and_with_condition(cond))
DBUG_RETURN(true);
}
}
DBUG_RETURN(false);
}
/*****************************************************************************
Remove calculation with tables that aren't yet read. Remove also tests
against fields that are read through key where the table is not a
outer join table.
We can't remove tests that are made against columns which are stored
in sorted order.
*****************************************************************************/
static Item *
part_of_refkey(TABLE *table, TABLE_REF *ref, Field *field)
{
uint ref_parts= ref->key_parts;
if (ref_parts)
{
if (ref->has_guarded_conds())
return NULL;
const KEY_PART_INFO *key_part= table->key_info[ref->key].key_part;
for (uint part=0 ; part < ref_parts ; part++,key_part++)
if (field->eq(key_part->field) &&
!(key_part->key_part_flag & HA_PART_KEY_SEG))
return ref->items[part];
}
return NULL;
}
/**
@return
1 if right_item is used removable reference key on left_item
@note see comments in make_cond_for_table_from_pred() about careful
usage/modifications of test_if_ref().
*/
static bool test_if_ref(Item *root_cond,
Item_field *left_item,Item *right_item)
{
if (left_item->depended_from)
return false; // don't even read join_tab of inner subquery!
Field *field=left_item->field;
JOIN_TAB *join_tab= field->table->reginfo.join_tab;
if (join_tab)
ASSERT_BEST_REF_IN_JOIN_ORDER(join_tab->join());
// No need to change const test
if (!field->table->const_table && join_tab &&
(join_tab->first_inner() == NO_PLAN_IDX ||
join_tab->join()->best_ref[join_tab->first_inner()]->join_cond() == root_cond) &&
/* "ref_or_null" implements "x=y or x is null", not "x=y" */
(join_tab->type() != JT_REF_OR_NULL))
{
Item *ref_item= part_of_refkey(field->table, &join_tab->ref(), field);
if (ref_item && ref_item->eq(right_item,1))
{
right_item= right_item->real_item();
if (right_item->type() == Item::FIELD_ITEM)
return (field->eq_def(((Item_field *) right_item)->field));
/* remove equalities injected by IN->EXISTS transformation */
else if (right_item->type() == Item::CACHE_ITEM)
return ((Item_cache *)right_item)->eq_def (field);
if (right_item->const_item() && !(right_item->is_null()))
{
/*
We can remove all fields except:
1. String data types:
- For BINARY/VARBINARY fields with equality against a
string: Ref access can return more rows than match the
string. The reason seems to be that the string constant
is not "padded" to the full length of the field when
setting up ref access. @todo Change how ref access for
BINARY/VARBINARY fields are done so that only qualifying
rows are returned from the storage engine.
2. Float data type: Comparison of float can differ
- When we search "WHERE field=value" using an index,
the "value" side is converted from double to float by
Field_float::store(), then two floats are compared.
- When we search "WHERE field=value" without indexes,
the "field" side is converted from float to double by
Field_float::val_real(), then two doubles are compared.
Note about string data types: All currently existing
collations have "PAD SPACE" style. If we introduce "NO PAD"
collations this function must return false for such
collations, because trailing space compression for indexes
makes the table value and the index value not equal to each
other in "NO PAD" collations. As index lookup strips
trailing spaces, it can return false candidates. Further
comparison of the actual table values is required.
*/
if (!((field->type() == MYSQL_TYPE_STRING || // 1
field->type() == MYSQL_TYPE_VARCHAR) && field->binary()) &&
!(field->type() == MYSQL_TYPE_FLOAT && field->decimals() > 0)) // 2
{
return !right_item->save_in_field_no_warnings(field, true);
}
}
}
}
return 0; // keep test
}
/*
Remove the predicates pushed down into the subquery
DESCRIPTION
Given that this join will be executed using (unique|index)_subquery,
without "checking NULL", remove the predicates that were pushed down
into the subquery.
If the subquery compares scalar values, we can remove the condition that
was wrapped into trig_cond (it will be checked when needed by the subquery
engine)
If the subquery compares row values, we need to keep the wrapped
equalities in the WHERE clause: when the left (outer) tuple has both NULL
and non-NULL values, we'll do a full table scan and will rely on the
equalities corresponding to non-NULL parts of left tuple to filter out
non-matching records.
If '*where' is a triggered condition, or contains 'OR x IS NULL', or
contains a condition coming from the original subquery's WHERE clause, or
if there are more than one outer expressions, then WHERE is not of the
simple form:
outer_expr = inner_expr
and thus this function does nothing.
If the index is on prefix (=> test_if_ref() is false), then the equality
is needed as post-filter, so this function does nothing.
TODO: We can remove the equalities that will be guaranteed to be true by the
fact that subquery engine will be using index lookup. This must be done only
for cases where there are no conversion errors of significance, e.g. 257
that is searched in a byte. But this requires homogenization of the return
codes of all Field*::store() methods.
*/
void JOIN::remove_subq_pushed_predicates()
{
if (where_cond->type() != Item::FUNC_ITEM)
return;
Item_func *const func= static_cast<Item_func *>(where_cond);
if (func->functype() == Item_func::EQ_FUNC &&
func->arguments()[0]->type() == Item::REF_ITEM &&
func->arguments()[1]->type() == Item::FIELD_ITEM &&
test_if_ref(func,
static_cast<Item_field *>(func->arguments()[1]),
func->arguments()[0]))
{
where_cond= NULL;
return;
}
}
/**
@brief
Add keys to derived tables'/views' result tables in a list
@param select_lex generate derived keys for select_lex's derived tables
@details
This function generates keys for all derived tables/views of the select_lex
to which this join corresponds to with help of the TABLE_LIST:generate_keys
function.
@return FALSE all keys were successfully added.
@return TRUE OOM error
*/
bool JOIN::generate_derived_keys()
{
assert(select_lex->materialized_derived_table_count);
for (TABLE_LIST *table= select_lex->leaf_tables;
table;
table= table->next_leaf)
{
table->derived_keys_ready= TRUE;
/* Process tables that aren't materialized yet. */
if (table->uses_materialization() && !table->table->is_created() &&
table->generate_keys())
return TRUE;
}
return FALSE;
}
/**
@brief
Drop unused keys for each materialized derived table/view
@details
For each materialized derived table/view, call TABLE::use_index to save one
index chosen by the optimizer and ignore others. If no key is chosen, then all
keys will be ignored.
*/
void JOIN::drop_unused_derived_keys()
{
assert(select_lex->materialized_derived_table_count);
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
for (uint i= 0 ; i < tables ; i++)
{
JOIN_TAB *tab= best_ref[i];
TABLE *table= tab->table();
/*
Save chosen key description if:
1) it's a materialized derived table
2) it's not yet instantiated
3) some keys are defined for it
*/
if (table &&
tab->table_ref->uses_materialization() && // (1)
!table->is_created() && // (2)
table->max_keys > 0) // (3)
{
Key_use *keyuse= tab->position()->key;
table->use_index(keyuse ? keyuse->key : -1);
const bool key_is_const= keyuse && tab->const_keys.is_set(keyuse->key);
tab->const_keys.clear_all();
tab->keys().clear_all();
if (!keyuse)
continue;
/*
Update the selected "keyuse" to point to key number 0.
Notice that unused keyuse entries still point to the deleted
candidate keys. tab->keys (and tab->const_keys if the chosen key
is constant) should reference key object no. 0 as well.
*/
tab->keys().set_bit(0);
if (key_is_const)
tab->const_keys.set_bit(0);
const uint oldkey= keyuse->key;
for (; keyuse->table_ref == tab->table_ref && keyuse->key == oldkey;
keyuse++)
keyuse->key= 0;
}
}
}
/**
Cache constant expressions in WHERE, HAVING, ON conditions.
@return False if success, True if error
@note This function is run after conditions have been pushed down to
individual tables, so transformation is applied to JOIN_TAB::condition
and not to the WHERE condition.
*/
bool JOIN::cache_const_exprs()
{
/* No need in cache if all tables are constant. */
assert(!plan_is_const());
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
for (uint i= const_tables; i < tables; i++)
{
Item *condition= best_ref[i]->condition();
if (condition == NULL)
continue;
Item *cache_item= NULL;
Item **analyzer_arg= &cache_item;
condition=
condition->compile(&Item::cache_const_expr_analyzer,
(uchar **)&analyzer_arg,
&Item::cache_const_expr_transformer,
(uchar *)&cache_item);
if (condition == NULL)
return true;
best_ref[i]->set_condition(condition);
}
if (having_cond)
{
Item *cache_item= NULL;
Item **analyzer_arg= &cache_item;
having_cond= having_cond->compile(&Item::cache_const_expr_analyzer,
(uchar **)&analyzer_arg,
&Item::cache_const_expr_transformer,
(uchar *)&cache_item);
if (having_cond == NULL)
return true;
}
return false;
}
/**
Extract a condition that can be checked after reading given table
@param cond Condition to analyze
@param tables Tables for which "current field values" are available
@param used_table Table(s) that we are extracting the condition for (may
also include PSEUDO_TABLE_BITS, and may be zero)
@param exclude_expensive_cond Do not push expensive conditions
@retval <>NULL Generated condition
@retval = NULL Already checked, OR error
@details
Extract the condition that can be checked after reading the table(s)
specified in @c used_table, given that current-field values for tables
specified in @c tables bitmap are available.
If @c used_table is 0, extract conditions for all tables in @c tables.
This function can be used to extract conditions relevant for a table
in a join order. Together with its caller, it will ensure that all
conditions are attached to the first table in the join order where all
necessary fields are available, and it will also ensure that a given
condition is attached to only one table.
To accomplish this, first initialize @c tables to the empty
set. Then, loop over all tables in the join order, set @c used_table to
the bit representing the current table, accumulate @c used_table into the
@c tables set, and call this function. To ensure correct handling of
const expressions and outer references, add the const table map and
OUTER_REF_TABLE_BIT to @c used_table for the first table. To ensure
that random expressions are evaluated for the final table, add
RAND_TABLE_BIT to @c used_table for the final table.
The function assumes that constant, inexpensive parts of the condition
have already been checked. Constant, expensive parts will be attached
to the first table in the join order, provided that the above call
sequence is followed.
The call order will ensure that conditions covering tables in @c tables
minus those in @c used_table, have already been checked.
The function takes into account that some parts of the condition are
guaranteed to be true by employed 'ref' access methods (the code that
does this is located at the end, search down for "EQ_FUNC").
@note
make_cond_for_info_schema() uses an algorithm similar to
make_cond_for_table().
*/
Item *
make_cond_for_table(Item *cond, table_map tables, table_map used_table,
bool exclude_expensive_cond)
{
return make_cond_for_table_from_pred(cond, cond, tables, used_table,
exclude_expensive_cond);
}
static Item *
make_cond_for_table_from_pred(Item *root_cond, Item *cond,
table_map tables, table_map used_table,
bool exclude_expensive_cond)
{
/*
Ignore this condition if
1. We are extracting conditions for a specific table, and
2. that table is not referenced by the condition, but not if
3. this is a constant condition not checked at optimization time and
this is the first table we are extracting conditions for.
(Assuming that used_table == tables for the first table.)
*/
if (used_table && // 1
!(cond->used_tables() & used_table) && // 2
!(cond->is_expensive() && used_table == tables)) // 3
return NULL;
if (cond->type() == Item::COND_ITEM)
{
if (((Item_cond*) cond)->functype() == Item_func::COND_AND_FUNC)
{
/* Create new top level AND item */
Item_cond_and *new_cond= new Item_cond_and;
if (!new_cond)
return NULL;
List_iterator<Item> li(*((Item_cond*) cond)->argument_list());
Item *item;
while ((item= li++))
{
Item *fix= make_cond_for_table_from_pred(root_cond, item,
tables, used_table,
exclude_expensive_cond);
if (fix)
new_cond->argument_list()->push_back(fix);
}
switch (new_cond->argument_list()->elements) {
case 0:
return NULL; // Always true
case 1:
return new_cond->argument_list()->head();
default:
if (new_cond->fix_fields(current_thd, NULL))
return NULL;
return new_cond;
}
}
else
{ // Or list
Item_cond_or *new_cond= new Item_cond_or;
if (!new_cond)
return NULL;
List_iterator<Item> li(*((Item_cond*) cond)->argument_list());
Item *item;
while ((item= li++))
{
Item *fix= make_cond_for_table_from_pred(root_cond, item,
tables, 0L,
exclude_expensive_cond);
if (!fix)
return NULL; // Always true
new_cond->argument_list()->push_back(fix);
}
if (new_cond->fix_fields(current_thd, NULL))
return NULL;
return new_cond;
}
}
/*
Omit this condition if
1. It has been marked as omittable before, or
2. Some tables referred by the condition are not available, or
3. We are extracting conditions for all tables, the condition is
considered 'expensive', and we want to delay evaluation of such
conditions to the execution phase.
*/
if (cond->marker == 3 || // 1
(cond->used_tables() & ~tables) || // 2
(!used_table && exclude_expensive_cond && cond->is_expensive())) // 3
return NULL;
/*
Extract this condition if
1. It has already been marked as applicable, or
2. It is not a <comparison predicate> (=, <, >, <=, >=, <=>)
*/
if (cond->marker == 2 || // 1
cond->eq_cmp_result() == Item::COND_OK) // 2
return cond;
/*
Remove equalities that are guaranteed to be true by use of 'ref' access
method.
Note that ref access implements "table1.field1 <=> table2.indexed_field2",
i.e. if it passed a NULL field1, it will return NULL indexed_field2 if
there are.
Thus the equality "table1.field1 = table2.indexed_field2",
is equivalent to "ref access AND table1.field1 IS NOT NULL"
i.e. "ref access and proper setting/testing of ref->null_rejecting".
Thus, we must be careful, that when we remove equalities below we also
set ref->null_rejecting, and test it at execution; otherwise wrong NULL
matches appear.
So:
- for the optimization phase, the code which is below, and the code in
test_if_ref(), and in add_key_field(), must be kept in sync: if the
applicability conditions in one place are relaxed, they should also be
relaxed elsewhere.
- for the execution phase, all possible execution methods must test
ref->null_rejecting.
*/
if (cond->type() == Item::FUNC_ITEM &&
((Item_func*) cond)->functype() == Item_func::EQ_FUNC)
{
Item *left_item= ((Item_func*) cond)->arguments()[0]->real_item();
Item *right_item= ((Item_func*) cond)->arguments()[1]->real_item();
if ((left_item->type() == Item::FIELD_ITEM &&
test_if_ref(root_cond, (Item_field*) left_item, right_item)) ||
(right_item->type() == Item::FIELD_ITEM &&
test_if_ref(root_cond, (Item_field*) right_item, left_item)))
{
cond->marker= 3; // Condition can be omitted
return NULL;
}
}
cond->marker= 2; // Mark condition as applicable
return cond;
}
/**
Separates the predicates in a join condition and pushes them to the
join step where all involved tables are available in the join prefix.
ON clauses from JOIN expressions are also pushed to the most appropriate step.
@param join Join object where predicates are pushed.
@param cond Pointer to condition which may contain an arbitrary number of
predicates, combined using AND, OR and XOR items.
If NULL, equivalent to a predicate that returns TRUE for all
row combinations.
@retval true Found impossible WHERE clause, or out-of-memory
@retval false Other
*/
static bool make_join_select(JOIN *join, Item *cond)
{
THD *thd= join->thd;
Opt_trace_context * const trace= &thd->opt_trace;
DBUG_ENTER("make_join_select");
ASSERT_BEST_REF_IN_JOIN_ORDER(join);
// Add IS NOT NULL conditions to table conditions:
add_not_null_conds(join);
/*
Extract constant conditions that are part of the WHERE clause.
Constant parts of join conditions from outer joins are attached to
the appropriate table condition in JOIN::attach_join_conditions().
*/
if (cond) /* Because of QUICK_GROUP_MIN_MAX_SELECT */
{ /* there may be a select without a cond. */
if (join->primary_tables > 1)
cond->update_used_tables(); // Table number may have changed
if (join->plan_is_const() &&
join->select_lex->master_unit() ==
thd->lex->unit) // The outer-most query block
join->const_table_map|= RAND_TABLE_BIT;
}
/*
Extract conditions that depend on constant tables.
The const part of the query's WHERE clause can be checked immediately
and if it is not satisfied then the join has empty result
*/
Item *const_cond= NULL;
if (cond)
const_cond= make_cond_for_table(cond, join->const_table_map,
(table_map) 0, true);
// Add conditions added by add_not_null_conds()
for (uint i= 0; i < join->const_tables; i++)
{
if (and_conditions(&const_cond, join->best_ref[i]->condition()))
DBUG_RETURN(true);
}
DBUG_EXECUTE("where", print_where(const_cond, "constants", QT_ORDINARY););
if (const_cond != NULL)
{
const bool const_cond_result= const_cond->val_int() != 0;
if (thd->is_error())
DBUG_RETURN(true);
Opt_trace_object trace_const_cond(trace);
trace_const_cond.add("condition_on_constant_tables", const_cond)
.add("condition_value", const_cond_result);
if (!const_cond_result)
{
DBUG_PRINT("info",("Found impossible WHERE condition"));
DBUG_RETURN(true);
}
}
/*
Extract remaining conditions from WHERE clause and join conditions,
and attach them to the most appropriate table condition. This means that
a condition will be evaluated as soon as all fields it depends on are
available. For outer join conditions, the additional criterion is that
we must have determined whether outer-joined rows are available, or
have been NULL-extended, see JOIN::attach_join_conditions() for details.
*/
{
Opt_trace_object trace_wrapper(trace);
Opt_trace_object
trace_conditions(trace, "attaching_conditions_to_tables");
trace_conditions.add("original_condition", cond);
Opt_trace_array
trace_attached_comp(trace, "attached_conditions_computation");
for (uint i=join->const_tables ; i < join->tables ; i++)
{
JOIN_TAB *const tab= join->best_ref[i];
if (!tab->position())
continue;
/*
first_inner is the X in queries like:
SELECT * FROM t1 LEFT OUTER JOIN (t2 JOIN t3) ON X
*/
const plan_idx first_inner= tab->first_inner();
const table_map used_tables= tab->prefix_tables();
const table_map current_map= tab->added_tables();
Item *tmp= NULL;
if (cond)
tmp= make_cond_for_table(cond,used_tables,current_map, 0);
/* Add conditions added by add_not_null_conds(). */
if (tab->condition() && and_conditions(&tmp, tab->condition()))
DBUG_RETURN(true);
if (cond && !tmp && tab->quick())
{ // Outer join
assert(tab->type() == JT_RANGE || tab->type() == JT_INDEX_MERGE);
/*
Hack to handle the case where we only refer to a table
in the ON part of an OUTER JOIN. In this case we want the code
below to check if we should use 'quick' instead.
*/
DBUG_PRINT("info", ("Item_int"));
tmp= new Item_int((longlong) 1,1); // Always true
}
if (tmp || !cond || tab->type() == JT_REF || tab->type() == JT_REF_OR_NULL ||
tab->type() == JT_EQ_REF || first_inner != NO_PLAN_IDX)
{
DBUG_EXECUTE("where",print_where(tmp,tab->table()->alias, QT_ORDINARY););
/*
If tab is an inner table of an outer join operation,
add a match guard to the pushed down predicate.
The guard will turn the predicate on only after
the first match for outer tables is encountered.
*/
if (cond && tmp)
{
/*
Because of QUICK_GROUP_MIN_MAX_SELECT there may be a select without
a cond, so neutralize the hack above.
*/
if (!(tmp= add_found_match_trig_cond(join, first_inner, tmp, NO_PLAN_IDX)))
DBUG_RETURN(true);
tab->set_condition(tmp);
/* Push condition to storage engine if this is enabled
and the condition is not guarded */
if (thd->optimizer_switch_flag(OPTIMIZER_SWITCH_ENGINE_CONDITION_PUSHDOWN) &&
first_inner == NO_PLAN_IDX)
{
Item *push_cond=
make_cond_for_table(tmp, tab->table_ref->map(),
tab->table_ref->map(), 0);
if (push_cond)
{
/* Push condition to handler */
if (!tab->table()->file->cond_push(push_cond))
tab->table()->file->pushed_cond= push_cond;
}
}
}
else
{
tab->set_condition(NULL);
}
DBUG_EXECUTE("where",print_where(tmp,tab->table()->alias, QT_ORDINARY););
if (tab->quick())
{
if (tab->needed_reg.is_clear_all() && tab->type() != JT_CONST)
{
/*
We keep (for now) the QUICK AM calculated in
get_quick_record_count().
*/
assert(tab->quick()->is_valid());
}
else
{
delete tab->quick();
tab->set_quick(NULL);
}
}
if ((tab->type() == JT_ALL || tab->type() == JT_RANGE ||
tab->type() == JT_INDEX_MERGE || tab->type() == JT_INDEX_SCAN) &&
tab->use_quick != QS_RANGE)
{
/*
We plan to scan (table/index/range scan).
Check again if we should use an index. We can use an index if:
1a) There is a condition that range optimizer can work on, and
1b) There are non-constant conditions on one or more keys, and
1c) Some of the non-constant fields may have been read
already. This may be the case if this is not the first
table in the join OR this is a subselect with
non-constant conditions referring to an outer table
(dependent subquery)
or,
2a) There are conditions only relying on constants
2b) This is the first non-constant table
2c) There is a limit of rows to read that is lower than
the fanout for this table, predicate filters included
(i.e., the estimated number of rows that will be
produced for this table per row combination of
previous tables)
2d) The query is NOT run with FOUND_ROWS() (because in that
case we have to scan through all rows to count them anyway)
*/
enum { DONT_RECHECK, NOT_FIRST_TABLE, LOW_LIMIT }
recheck_reason= DONT_RECHECK;
assert(tab->const_keys.is_subset(tab->keys()));
const join_type orig_join_type= tab->type();
const QUICK_SELECT_I *const orig_quick= tab->quick();
if (cond && // 1a
(tab->keys() != tab->const_keys) && // 1b
(i > 0 || // 1c
(join->select_lex->master_unit()->item &&
cond->used_tables() & OUTER_REF_TABLE_BIT)))
recheck_reason= NOT_FIRST_TABLE;
else if (!tab->const_keys.is_clear_all() && // 2a
i == join->const_tables && // 2b
(join->unit->select_limit_cnt <
(tab->position()->rows_fetched *
tab->position()->filter_effect)) && // 2c
!join->calc_found_rows) // 2d
recheck_reason= LOW_LIMIT;
if (tab->position()->sj_strategy == SJ_OPT_LOOSE_SCAN)
{
/*
Semijoin loose scan has settled for a certain index-based access
method with suitable characteristics, don't substitute it.
*/
recheck_reason= DONT_RECHECK;
}
if (recheck_reason != DONT_RECHECK)
{
Opt_trace_object trace_one_table(trace);
trace_one_table.add_utf8_table(tab->table_ref);
Opt_trace_object trace_table(trace, "rechecking_index_usage");
if (recheck_reason == NOT_FIRST_TABLE)
trace_table.add_alnum("recheck_reason", "not_first_table");
else
trace_table.add_alnum("recheck_reason", "low_limit").
add("limit", join->unit->select_limit_cnt).
add("row_estimate",
tab->position()->rows_fetched *
tab->position()->filter_effect);
/* Join with outer join condition */
Item *orig_cond= tab->condition();
tab->and_with_condition(tab->join_cond());
/*
We can't call sel->cond->fix_fields,
as it will break tab->join_cond() if it's AND condition
(fix_fields currently removes extra AND/OR levels).
Yet attributes of the just built condition are not needed.
Thus we call sel->cond->quick_fix_field for safety.
*/
if (tab->condition() && !tab->condition()->fixed)
tab->condition()->quick_fix_field();
key_map usable_keys= tab->keys();
ORDER::enum_order interesting_order= ORDER::ORDER_NOT_RELEVANT;
if (recheck_reason == LOW_LIMIT)
{
int read_direction= 0;
/*
If the current plan is to use range, then check if the
already selected index provides the order dictated by the
ORDER BY clause.
*/
if (tab->quick() && tab->quick()->index != MAX_KEY)
{
const uint ref_key= tab->quick()->index;
read_direction= test_if_order_by_key(join->order,
tab->table(), ref_key);
/*
If the index provides order there is no need to recheck
index usage; we already know from the former call to
test_quick_select() that a range scan on the chosen
index is cheapest. Note that previous calls to
test_quick_select() did not take order direction
(ASC/DESC) into account, so in case of DESC ordering
we still need to recheck.
*/
if ((read_direction == 1) ||
(read_direction == -1 && tab->quick()->reverse_sorted()))
{
recheck_reason= DONT_RECHECK;
}
}
/*
We do a cost based search for an ordering index here. Do this
only if prefer_ordering_index switch is on or an index is
forced for order by
*/
if (recheck_reason != DONT_RECHECK &&
(tab->table()->force_index_order ||
thd->optimizer_switch_flag(
OPTIMIZER_SWITCH_PREFER_ORDERING_INDEX)))
{
int best_key= -1;
ha_rows select_limit= join->unit->select_limit_cnt;
/* Use index specified in FORCE INDEX FOR ORDER BY, if any. */
if (tab->table()->force_index)
usable_keys.intersect(tab->table()->keys_in_use_for_order_by);
/* Do a cost based search on the indexes that give sort order */
test_if_cheaper_ordering(tab, join->order, tab->table(),
usable_keys, -1, select_limit,
&best_key, &read_direction,
&select_limit);
if (best_key < 0)
recheck_reason= DONT_RECHECK; // No usable keys
else
{
// Only usable_key is the best_key chosen
usable_keys.clear_all();
usable_keys.set_bit(best_key);
interesting_order= (read_direction == -1 ? ORDER::ORDER_DESC :
ORDER::ORDER_ASC);
}
}
}
bool search_if_impossible= recheck_reason != DONT_RECHECK;
if (search_if_impossible)
{
if (tab->quick())
{
delete tab->quick();
tab->set_type(JT_ALL);
}
QUICK_SELECT_I *qck;
search_if_impossible=
test_quick_select(thd, usable_keys,
used_tables & ~tab->table_ref->map(),
join->calc_found_rows ?
HA_POS_ERROR :
join->unit->select_limit_cnt,
false, // don't force quick range
interesting_order, tab,
tab->condition(),
&tab->needed_reg, &qck,
tab->table()->force_index) < 0;
tab->set_quick(qck);
}
tab->set_condition(orig_cond);
if (search_if_impossible)
{
/*
Before reporting "Impossible WHERE" for the whole query
we have to check isn't it only "impossible ON" instead
*/
if (!tab->join_cond())
DBUG_RETURN(1); // No ON, so it's really "impossible WHERE"
Opt_trace_object trace_without_on(trace, "without_ON_clause");
if (tab->quick())
{
delete tab->quick();
tab->set_type(JT_ALL);
}
QUICK_SELECT_I *qck;
const bool impossible_where=
test_quick_select(thd, tab->keys(),
used_tables & ~tab->table_ref->map(),
join->calc_found_rows ?
HA_POS_ERROR :
join->unit->select_limit_cnt,
false, //don't force quick range
ORDER::ORDER_NOT_RELEVANT, tab,
tab->condition(), &tab->needed_reg,
&qck, tab->table()->force_index) < 0;
tab->set_quick(qck);
if (impossible_where)
DBUG_RETURN(1); // Impossible WHERE
}
/*
Access method changed. This is after deciding join order
and access method for all other tables so the info
updated below will not have any effect on the execution
plan.
*/
if (tab->quick())
tab->set_type(calc_join_type(tab->quick()->get_type()));
} // end of "if (recheck_reason != DONT_RECHECK)"
if (!tab->table()->quick_keys.is_subset(tab->checked_keys) ||
!tab->needed_reg.is_subset(tab->checked_keys))
{
tab->keys().merge(tab->table()->quick_keys);
tab->keys().merge(tab->needed_reg);
/*
The logic below for assigning tab->use_quick is strange.
It bases the decision of which access method to use
(dynamic range, range, scan) based on seemingly
unrelated information like the presense of another index
with too bad selectivity to be used.
Consider the following scenario:
The join optimizer has decided to use join order
(t1,t2), and 'tab' is currently t2. Further, assume that
there is a join condition between t1 and t2 using some
range operator (e.g. "t1.x < t2.y").
It has been decided that a table scan is best for t2.
make_join_select() then reran the range optimizer a few
lines up because there is an index 't2.good_idx'
covering the t2.y column. If 'good_idx' is the only
index in t2, the decision below will be to use dynamic
range. However, if t2 also has another index 't2.other'
which the range access method can be used on but
selectivity is bad (#rows estimate is high), then table
scan is chosen instead.
Thus, the choice of DYNAMIC RANGE vs SCAN depends on the
presense of an index that has so bad selectivity that it
will not be used anyway.
*/
if (!tab->needed_reg.is_clear_all() &&
(tab->table()->quick_keys.is_clear_all() ||
(tab->quick() &&
(tab->quick()->records >= 100L))))
{
tab->use_quick= QS_DYNAMIC_RANGE;
tab->set_type(JT_ALL);
}
else
tab->use_quick= QS_RANGE;
}
if (tab->type() != orig_join_type ||
tab->quick() != orig_quick) // Access method changed
tab->position()->filter_effect= COND_FILTER_STALE;
}
}
if (join->attach_join_conditions(i))
DBUG_RETURN(true);
}
trace_attached_comp.end();
/*
In outer joins the loop above, in iteration for table #i, may push
conditions to a table before #i. Thus, the processing below has to be in
a separate loop:
*/
Opt_trace_array trace_attached_summary(trace,
"attached_conditions_summary");
for (uint i= join->const_tables ; i < join->tables ; i++)
{
JOIN_TAB * const tab= join->best_ref[i];
if (!tab->table())
continue;
Item * const cond= tab->condition();
Opt_trace_object trace_one_table(trace);
trace_one_table.add_utf8_table(tab->table_ref).
add("attached", cond);
if (cond &&
cond->has_subquery() /* traverse only if needed */ )
{
/*
Why we pass walk_subquery=false: imagine
WHERE t1.col IN (SELECT * FROM t2
WHERE t2.col IN (SELECT * FROM t3)
and tab==t1. The grandchild subquery (SELECT * FROM t3) should not
be marked as "in condition of t1" but as "in condition of t2", for
correct calculation of the number of its executions.
*/
std::pair<SELECT_LEX *, int> pair_object(join->select_lex, i);
cond->walk(&Item::inform_item_in_cond_of_tab,
Item::WALK_POSTFIX,
pointer_cast<uchar * const>(&pair_object));
}
}
}
DBUG_RETURN(0);
}
/**
Remove the following expressions from ORDER BY and GROUP BY:
Constant expressions @n
Expression that only uses tables that are of type EQ_REF and the reference
is in the ORDER list or if all refereed tables are of the above type.
In the following, the X field can be removed:
@code
SELECT * FROM t1,t2 WHERE t1.a=t2.a ORDER BY t1.a,t2.X
SELECT * FROM t1,t2,t3 WHERE t1.a=t2.a AND t2.b=t3.b ORDER BY t1.a,t3.X
@endcode
These can't be optimized:
@code
SELECT * FROM t1,t2 WHERE t1.a=t2.a ORDER BY t2.X,t1.a
SELECT * FROM t1,t2 WHERE t1.a=t2.a AND t1.b=t2.b ORDER BY t1.a,t2.c
SELECT * FROM t1,t2 WHERE t1.a=t2.a ORDER BY t2.b,t1.a
@endcode
@param JOIN join object
@param start_order clause being analyzed (ORDER BY, GROUP BY...)
@param tab table
@param cached_eq_ref_tables bitmap: bit Z is set if the table of map Z
was already the subject of an eq_ref_table() call for the same clause; then
the return value of this previous call can be found at bit Z of
'eq_ref_tables'
@param eq_ref_tables see above.
*/
static bool
eq_ref_table(JOIN *join, ORDER *start_order, JOIN_TAB *tab,
table_map *cached_eq_ref_tables, table_map *eq_ref_tables)
{
/* We can skip const tables only if not an outer table */
if (tab->type() == JT_CONST && tab->first_inner() == NO_PLAN_IDX)
return true;
if (tab->type() != JT_EQ_REF || tab->table()->is_nullable())
return false;
const table_map map= tab->table_ref->map();
uint found= 0;
for (Item **ref_item= tab->ref().items, **end= ref_item + tab->ref().key_parts ;
ref_item != end ; ref_item++)
{
if (! (*ref_item)->const_item())
{ // Not a const ref
ORDER *order;
for (order=start_order ; order ; order=order->next)
{
if ((*ref_item)->eq(order->item[0],0))
break;
}
if (order)
{
if (!(order->used & map))
{
found++;
order->used|= map;
}
continue; // Used in ORDER BY
}
if (!only_eq_ref_tables(join, start_order, (*ref_item)->used_tables(),
cached_eq_ref_tables, eq_ref_tables))
return false;
}
}
/* Check that there was no reference to table before sort order */
for (; found && start_order ; start_order=start_order->next)
{
if (start_order->used & map)
{
found--;
continue;
}
if (start_order->depend_map & map)
return false;
}
return true;
}
/// @see eq_ref_table()
static bool
only_eq_ref_tables(JOIN *join, ORDER *order, table_map tables,
table_map *cached_eq_ref_tables, table_map *eq_ref_tables)
{
tables&= ~PSEUDO_TABLE_BITS;
for (JOIN_TAB **tab=join->map2table ; tables ; tab++, tables>>=1)
{
if (tables & 1)
{
const table_map map= (*tab)->table_ref->map();
bool is_eq_ref;
if (*cached_eq_ref_tables & map) // then there exists a cached bit
is_eq_ref= *eq_ref_tables & map;
else
{
is_eq_ref= eq_ref_table(join, order, *tab,
cached_eq_ref_tables, eq_ref_tables);
if (is_eq_ref)
*eq_ref_tables|= map;
else
*eq_ref_tables&= ~map;
*cached_eq_ref_tables|= map; // now there exists a cached bit
}
if (!is_eq_ref)
return false;
}
}
return true;
}
/**
Check if an expression in ORDER BY or GROUP BY is a duplicate of a
preceding expression.
@param first_order the first expression in the ORDER BY or
GROUP BY clause
@param possible_dup the expression that might be a duplicate of
another expression preceding it the ORDER BY
or GROUP BY clause
@returns true if possible_dup is a duplicate, false otherwise
*/
static bool duplicate_order(const ORDER *first_order,
const ORDER *possible_dup)
{
const ORDER *order;
for (order=first_order; order ; order=order->next)
{
if (order == possible_dup)
{
// all expressions preceding possible_dup have been checked.
return false;
}
else
{
const Item *it1= order->item[0]->real_item();
const Item *it2= possible_dup->item[0]->real_item();
if (it1->eq(it2, 0))
return true;
}
}
return false;
}
/**
Remove all constants and check if ORDER only contains simple
expressions.
simple_order is set to 1 if sort_order only uses fields from head table
and the head table is not a LEFT JOIN table.
@param first_order List of SORT or GROUP order
@param cond WHERE statement
@param change_list Set to 1 if we should remove things from list.
If this is not set, then only simple_order is
calculated.
@param simple_order Set to 1 if we are only using simple expressions
@param clause_type "ORDER BY" etc for printing in optimizer trace
@return
Returns new sort order
*/
ORDER *JOIN::remove_const(ORDER *first_order, Item *cond, bool change_list,
bool *simple_order, const char *clause_type)
{
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
if (plan_is_const())
return change_list ? 0 : first_order; // No need to sort
Opt_trace_context * const trace= &thd->opt_trace;
Opt_trace_disable_I_S trace_disabled(trace, first_order == NULL);
Opt_trace_object trace_wrapper(trace);
Opt_trace_object trace_simpl(trace, "clause_processing");
if (trace->is_started())
{
trace_simpl.add_alnum("clause", clause_type);
String str;
st_select_lex::print_order(&str, first_order,
enum_query_type(QT_TO_SYSTEM_CHARSET |
QT_SHOW_SELECT_NUMBER |
QT_NO_DEFAULT_DB));
trace_simpl.add_utf8("original_clause", str.ptr(), str.length());
}
Opt_trace_array trace_each_item(trace, "items");
ORDER *order,**prev_ptr;
JOIN_TAB *const first_tab= best_ref[const_tables];
table_map first_table= first_tab->table_ref->map();
table_map not_const_tables= ~const_table_map;
table_map ref;
// Caches to avoid repeating eq_ref_table() calls, @see eq_ref_table()
table_map eq_ref_tables= 0, cached_eq_ref_tables= 0;
DBUG_ENTER("JOIN::remove_const");
prev_ptr= &first_order;
*simple_order= !first_tab->join_cond();
/* NOTE: A variable of not_const_tables ^ first_table; breaks gcc 2.7 */
update_depend_map(first_order);
for (order=first_order; order ; order=order->next)
{
Opt_trace_object trace_one_item(trace);
trace_one_item.add("item", order->item[0]);
table_map order_tables=order->item[0]->used_tables();
if (order->item[0]->with_sum_func ||
/*
If the outer table of an outer join is const (either by itself or
after applying WHERE condition), grouping on a field from such a
table will be optimized away and filesort without temporary table
will be used unless we prevent that now. Filesort is not fit to
handle joins and the join condition is not applied. We can't detect
the case without an expensive test, however, so we force temporary
table for all queries containing more than one table, ROLLUP, and an
outer join.
*/
(primary_tables > 1 &&
rollup.state == ROLLUP::STATE_INITED &&
select_lex->outer_join))
*simple_order= 0; // Must do a temp table to sort
else if (!(order_tables & not_const_tables))
{
if (order->item[0]->has_subquery())
{
if (!thd->lex->is_explain())
{
Opt_trace_array trace_subselect(trace, "subselect_evaluation");
order->item[0]->val_str(&order->item[0]->str_value);
}
order->item[0]->mark_subqueries_optimized_away();
}
trace_one_item.add("uses_only_constant_tables", true);
continue; // skip const item
}
else if (duplicate_order(first_order, order))
{
/*
If 'order' is a duplicate of an expression earlier in the
ORDER/GROUP BY sequence, it can be removed from the ORDER BY
or GROUP BY clause.
*/
trace_one_item.add("duplicate_item", true);
continue;
}
else if (order->in_field_list && order->item[0]->has_subquery())
/*
If the order item is a subquery that is also in the field
list, a temp table should be used to avoid evaluating the
subquery for each row both when a) creating a sort index and
b) getting the value.
Example: "SELECT (SELECT ... ) as a ... GROUP BY a;"
*/
*simple_order= false;
else
{
if (order_tables & (RAND_TABLE_BIT | OUTER_REF_TABLE_BIT))
*simple_order=0;
else
{
if (cond && const_expression_in_where(cond,order->item[0]))
{
trace_one_item.add("equals_constant_in_where", true);
continue;
}
if ((ref=order_tables & (not_const_tables ^ first_table)))
{
if (!(order_tables & first_table) &&
only_eq_ref_tables(this, first_order, ref,
&cached_eq_ref_tables, &eq_ref_tables))
{
trace_one_item.add("eq_ref_to_preceding_items", true);
continue;
}
*simple_order=0; // Must do a temp table to sort
}
}
}
if (change_list)
*prev_ptr= order; // use this entry
prev_ptr= &order->next;
}
if (change_list)
*prev_ptr=0;
if (prev_ptr == &first_order) // Nothing to sort/group
*simple_order=1;
DBUG_PRINT("exit",("simple_order: %d",(int) *simple_order));
trace_each_item.end();
trace_simpl.add("resulting_clause_is_simple", *simple_order);
if (trace->is_started() && change_list)
{
String str;
st_select_lex::print_order(&str, first_order,
enum_query_type(QT_TO_SYSTEM_CHARSET |
QT_SHOW_SELECT_NUMBER |
QT_NO_DEFAULT_DB));
trace_simpl.add_utf8("resulting_clause", str.ptr(), str.length());
}
DBUG_RETURN(first_order);
}
/**
Optimize conditions by
a) applying transitivity to build multiple equality predicates
(MEP): if x=y and y=z the MEP x=y=z is built.
b) apply constants where possible. If the value of x is known to be
42, x is replaced with a constant of value 42. By transitivity, this
also applies to MEPs, so the MEP in a) will become 42=x=y=z.
c) remove conditions that are always false or always true
@param thd Thread handler
@param[in,out] cond WHERE or HAVING condition to optimize
@param[out] cond_equal The built multiple equalities
@param join_list list of join operations with join conditions
= NULL: Called for HAVING condition
@param[out] cond_value Not changed if cond was empty
COND_TRUE if cond is always true
COND_FALSE if cond is impossible
COND_OK otherwise
@returns false if success, true if error
*/
bool optimize_cond(THD *thd, Item **cond, COND_EQUAL **cond_equal,
List<TABLE_LIST> *join_list,
Item::cond_result *cond_value)
{
Opt_trace_context * const trace= &thd->opt_trace;
DBUG_ENTER("optimize_cond");
Opt_trace_object trace_wrapper(trace);
Opt_trace_object trace_cond(trace, "condition_processing");
trace_cond.add_alnum("condition", join_list ? "WHERE" : "HAVING");
trace_cond.add("original_condition", *cond);
Opt_trace_array trace_steps(trace, "steps");
/*
Enter this function
a) For a WHERE condition or a query having outer join.
b) For a HAVING condition.
*/
assert(*cond || join_list);
/*
Build all multiple equality predicates and eliminate equality
predicates that can be inferred from these multiple equalities.
For each reference of a field included into a multiple equality
that occurs in a function set a pointer to the multiple equality
predicate. Substitute a constant instead of this field if the
multiple equality contains a constant.
This is performed for the WHERE condition and any join conditions, but
not for the HAVING condition.
*/
if (join_list)
{
Opt_trace_object step_wrapper(trace);
step_wrapper.add_alnum("transformation", "equality_propagation");
{
Opt_trace_disable_I_S
disable_trace_wrapper(trace, !(*cond && (*cond)->has_subquery()));
Opt_trace_array
trace_subselect(trace, "subselect_evaluation");
if (build_equal_items(thd, *cond, cond, NULL, true,
join_list, cond_equal))
DBUG_RETURN(true);
}
step_wrapper.add("resulting_condition", *cond);
}
/* change field = field to field = const for each found field = const */
if (*cond)
{
Opt_trace_object step_wrapper(trace);
step_wrapper.add_alnum("transformation", "constant_propagation");
{
Opt_trace_disable_I_S
disable_trace_wrapper(trace, !(*cond)->has_subquery());
Opt_trace_array trace_subselect(trace, "subselect_evaluation");
if (propagate_cond_constants(thd, NULL, *cond, *cond))
DBUG_RETURN(true);
}
step_wrapper.add("resulting_condition", *cond);
}
/*
Remove all instances of item == item
Remove all and-levels where CONST item != CONST item
*/
DBUG_EXECUTE("where",print_where(*cond,"after const change", QT_ORDINARY););
if (*cond)
{
Opt_trace_object step_wrapper(trace);
step_wrapper.add_alnum("transformation", "trivial_condition_removal");
{
Opt_trace_disable_I_S
disable_trace_wrapper(trace, !(*cond)->has_subquery());
Opt_trace_array trace_subselect(trace, "subselect_evaluation");
if (remove_eq_conds(thd, *cond, cond, cond_value))
DBUG_RETURN(true);
}
step_wrapper.add("resulting_condition", *cond);
}
assert(!thd->is_error());
if (thd->is_error())
DBUG_RETURN(true);
DBUG_RETURN(false);
}
/**
Handle the recursive job for remove_eq_conds()
@param thd Thread handler
@param cond the condition to handle.
@param[out] retcond Modified condition after removal
@param[out] cond_value the resulting value of the condition
@see remove_eq_conds() for more details on argument
@returns false if success, true if error
*/
static bool internal_remove_eq_conds(THD *thd, Item *cond,
Item **retcond,
Item::cond_result *cond_value)
{
if (cond->type() == Item::COND_ITEM)
{
Item_cond *const item_cond= down_cast<Item_cond *>(cond);
const bool and_level= item_cond->functype() == Item_func::COND_AND_FUNC;
List_iterator<Item> li(*item_cond->argument_list());
bool should_fix_fields= false;
*cond_value=Item::COND_UNDEF;
Item *item;
while ((item=li++))
{
Item *new_item;
Item::cond_result tmp_cond_value;
if (internal_remove_eq_conds(thd, item, &new_item, &tmp_cond_value))
return true;
if (new_item == NULL)
li.remove();
else if (item != new_item)
{
(void) li.replace(new_item);
should_fix_fields= true;
}
if (*cond_value == Item::COND_UNDEF)
*cond_value= tmp_cond_value;
switch (tmp_cond_value)
{
case Item::COND_OK: // Not TRUE or FALSE
if (and_level || *cond_value == Item::COND_FALSE)
*cond_value= tmp_cond_value;
break;
case Item::COND_FALSE:
if (and_level) // Always false
{
*cond_value= tmp_cond_value;
*retcond= NULL;
return false;
}
break;
case Item::COND_TRUE:
if (!and_level) // Always true
{
*cond_value= tmp_cond_value;
*retcond= NULL;
return false;
}
break;
case Item::COND_UNDEF: // Impossible
assert(false); /* purecov: deadcode */
}
}
if (should_fix_fields)
item_cond->update_used_tables();
if (item_cond->argument_list()->elements == 0 ||
*cond_value != Item::COND_OK)
{
*retcond= NULL;
return false;
}
if (item_cond->argument_list()->elements == 1)
{
/*
BUG#11765699:
We're dealing with an AND or OR item that has only one
argument. However, it is not an option to empty the list
because:
- this function is called for either JOIN::conds or
JOIN::having, but these point to the same condition as
SELECT_LEX::where and SELECT_LEX::having do.
- The return value of remove_eq_conds() is assigned to
JOIN::conds and JOIN::having, so emptying the list and
returning the only remaining item "replaces" the AND or OR
with item for the variables in JOIN. However, the return
value is not assigned to the SELECT_LEX counterparts. Thus,
if argument_list is emptied, SELECT_LEX forgets the item in
argument_list()->head().
item is therefore returned, but argument_list is not emptied.
*/
item= item_cond->argument_list()->head();
/*
Consider reenabling the line below when the optimizer has been
split into properly separated phases.
item_cond->argument_list()->empty();
*/
*retcond= item;
return false;
}
}
else if (cond->type() == Item::FUNC_ITEM &&
down_cast<Item_func *>(cond)->functype() == Item_func::ISNULL_FUNC)
{
Item_func_isnull *const func= down_cast<Item_func_isnull *>(cond);
Item **args= func->arguments();
if (args[0]->type() == Item::FIELD_ITEM)
{
Field *const field= down_cast<Item_field *>(args[0])->field;
/* fix to replace 'NULL' dates with '0' ([email protected]) */
/*
See BUG#12594011
Documentation says that
SELECT datetime_notnull d FROM t1 WHERE d IS NULL
shall return rows where d=='0000-00-00'
Thus, for DATE and DATETIME columns defined as NOT NULL,
"date_notnull IS NULL" has to be modified to
"date_notnull IS NULL OR date_notnull == 0" (if outer join)
"date_notnull == 0" (otherwise)
*/
if (((field->type() == MYSQL_TYPE_DATE) ||
(field->type() == MYSQL_TYPE_DATETIME)) &&
(field->flags & NOT_NULL_FLAG))
{
Item *item0= new(thd->mem_root) Item_int((longlong)0, 1);
if (item0 == NULL)
return true;
Item *eq_cond= new(thd->mem_root) Item_func_eq(args[0], item0);
if (eq_cond == NULL)
return true;
if (args[0]->is_outer_field())
{
// outer join: transform "col IS NULL" to "col IS NULL or col=0"
Item *or_cond= new(thd->mem_root) Item_cond_or(eq_cond, cond);
if (or_cond == NULL)
return true;
cond= or_cond;
}
else
{
// not outer join: transform "col IS NULL" to "col=0"
cond= eq_cond;
}
if (cond->fix_fields(thd, &cond))
return true;
}
}
if (cond->const_item())
{
bool value;
if (eval_const_cond(thd, cond, &value))
return true;
*cond_value= value ? Item::COND_TRUE : Item::COND_FALSE;
*retcond= NULL;
return false;
}
}
else if (cond->const_item() && !cond->is_expensive())
{
bool value;
if (eval_const_cond(thd, cond, &value))
return true;
*cond_value= value ? Item::COND_TRUE : Item::COND_FALSE;
*retcond= NULL;
return false;
}
else
{ // boolan compare function
*cond_value= cond->eq_cmp_result();
if (*cond_value == Item::COND_OK)
{
*retcond= cond;
return false;
}
Item *left_item= down_cast<Item_func *>(cond)->arguments()[0];
Item *right_item= down_cast<Item_func *>(cond)->arguments()[1];
if (left_item->eq(right_item,1))
{
if (!left_item->maybe_null ||
down_cast<Item_func *>(cond)->functype() == Item_func::EQUAL_FUNC)
{
*retcond= NULL;
return false; // Compare of identical items
}
}
}
*cond_value= Item::COND_OK;
*retcond= cond; // Point at next and level
return false;
}
/**
Remove const and eq items. Return new item, or NULL if no condition
@param thd thread handler
@param cond the condition to handle
@param[out] retcond condition after const removal
@param[out] cond_value resulting value of the condition
=COND_OK condition must be evaluated (e.g field = constant)
=COND_TRUE always true (e.g 1 = 1)
=COND_FALSE always false (e.g 1 = 2)
@note calls internal_remove_eq_conds() to check the complete tree.
@returns false if success, true if error
*/
bool remove_eq_conds(THD *thd, Item *cond, Item **retcond,
Item::cond_result *cond_value)
{
if (cond->type() == Item::FUNC_ITEM &&
down_cast<Item_func *>(cond)->functype() == Item_func::ISNULL_FUNC)
{
/*
Handles this special case for some ODBC applications:
The are requesting the row that was just updated with a auto_increment
value with this construct:
SELECT * from table_name where auto_increment_column IS NULL
This will be changed to:
SELECT * from table_name where auto_increment_column = LAST_INSERT_ID
*/
Item_func_isnull *const func= down_cast<Item_func_isnull *>(cond);
Item **args= func->arguments();
if (args[0]->type() == Item::FIELD_ITEM)
{
Field *const field= down_cast<Item_field *>(args[0])->field;
if ((field->flags & AUTO_INCREMENT_FLAG) &&
!field->table->is_nullable() &&
(thd->variables.option_bits & OPTION_AUTO_IS_NULL) &&
(thd->first_successful_insert_id_in_prev_stmt > 0 &&
thd->substitute_null_with_insert_id))
{
query_cache.abort(&thd->query_cache_tls);
cond= new Item_func_eq(
args[0],
new Item_int(NAME_STRING("last_insert_id()"),
thd->read_first_successful_insert_id_in_prev_stmt(),
MY_INT64_NUM_DECIMAL_DIGITS));
if (cond == NULL)
return true;
if (cond->fix_fields(thd, &cond))
return true;
/*
IS NULL should be mapped to LAST_INSERT_ID only for first row, so
clear for next row
*/
thd->substitute_null_with_insert_id= FALSE;
*cond_value= Item::COND_OK;
*retcond= cond;
return false;
}
}
}
return internal_remove_eq_conds(thd, cond, retcond, cond_value);
}
/**
Check if GROUP BY/DISTINCT can be optimized away because the set is
already known to be distinct.
Used in removing the GROUP BY/DISTINCT of the following types of
statements:
@code
SELECT [DISTINCT] <unique_key_cols>... FROM <single_table_ref>
[GROUP BY <unique_key_cols>,...]
@endcode
If (a,b,c is distinct)
then <any combination of a,b,c>,{whatever} is also distinct
This function checks if all the key parts of any of the unique keys
of the table are referenced by a list : either the select list
through find_field_in_item_list or GROUP BY list through
find_field_in_order_list.
If the above holds and the key parts cannot contain NULLs then we
can safely remove the GROUP BY/DISTINCT,
as no result set can be more distinct than an unique key.
@param tab The join table to operate on.
@param find_func function to iterate over the list and search
for a field
@retval
1 found
@retval
0 not found.
@note
The function assumes that make_outerjoin_info() has been called in
order for the check for outer tables to work.
*/
static bool
list_contains_unique_index(JOIN_TAB *tab,
bool (*find_func) (Field *, void *), void *data)
{
TABLE *table= tab->table();
if (tab->is_inner_table_of_outer_join())
return 0;
for (uint keynr= 0; keynr < table->s->keys; keynr++)
{
if (keynr == table->s->primary_key ||
(table->key_info[keynr].flags & HA_NOSAME))
{
KEY *keyinfo= table->key_info + keynr;
KEY_PART_INFO *key_part, *key_part_end;
for (key_part=keyinfo->key_part,
key_part_end=key_part+ keyinfo->user_defined_key_parts;
key_part < key_part_end;
key_part++)
{
if (key_part->field->real_maybe_null() ||
!find_func(key_part->field, data))
break;
}
if (key_part == key_part_end)
return 1;
}
}
return 0;
}
/**
Helper function for list_contains_unique_index.
Find a field reference in a list of ORDER structures.
Finds a direct reference of the Field in the list.
@param field The field to search for.
@param data ORDER *.The list to search in
@retval
1 found
@retval
0 not found.
*/
static bool
find_field_in_order_list (Field *field, void *data)
{
ORDER *group= (ORDER *) data;
bool part_found= 0;
for (ORDER *tmp_group= group; tmp_group; tmp_group=tmp_group->next)
{
Item *item= (*tmp_group->item)->real_item();
if (item->type() == Item::FIELD_ITEM &&
((Item_field*) item)->field->eq(field))
{
part_found= 1;
break;
}
}
return part_found;
}
/**
Helper function for list_contains_unique_index.
Find a field reference in a dynamic list of Items.
Finds a direct reference of the Field in the list.
@param[in] field The field to search for.
@param[in] data List<Item> *.The list to search in
@retval
1 found
@retval
0 not found.
*/
static bool
find_field_in_item_list (Field *field, void *data)
{
List<Item> *fields= (List<Item> *) data;
bool part_found= 0;
List_iterator<Item> li(*fields);
Item *item;
while ((item= li++))
{
if (item->type() == Item::FIELD_ITEM &&
((Item_field*) item)->field->eq(field))
{
part_found= 1;
break;
}
}
return part_found;
}
/**
Create a group by that consist of all non const fields.
Try to use the fields in the order given by 'order' to allow one to
optimize away 'order by'.
*/
static ORDER *
create_distinct_group(THD *thd, Ref_ptr_array ref_pointer_array,
ORDER *order_list, List<Item> &fields,
List<Item> &all_fields,
bool *all_order_by_fields_used)
{
List_iterator<Item> li(fields);
Item *item;
ORDER *order,*group,**prev;
*all_order_by_fields_used= 1;
while ((item=li++))
item->marker=0; /* Marker that field is not used */
prev= &group; group=0;
for (order=order_list ; order; order=order->next)
{
if (order->in_field_list)
{
ORDER *ord=(ORDER*) thd->memdup((char*) order,sizeof(ORDER));
if (!ord)
return 0;
*prev=ord;
prev= &ord->next;
(*ord->item)->marker=1;
}
else
*all_order_by_fields_used= 0;
}
li.rewind();
while ((item=li++))
{
if (!item->const_item() && !item->with_sum_func && !item->marker)
{
/*
Don't put duplicate columns from the SELECT list into the
GROUP BY list.
*/
ORDER *ord_iter;
for (ord_iter= group; ord_iter; ord_iter= ord_iter->next)
if ((*ord_iter->item)->eq(item, 1))
goto next_item;
ORDER *ord=(ORDER*) thd->mem_calloc(sizeof(ORDER));
if (!ord)
return 0;
if (item->type() == Item::FIELD_ITEM &&
item->field_type() == MYSQL_TYPE_BIT)
{
/*
Because HEAP tables can't index BIT fields we need to use an
additional hidden field for grouping because later it will be
converted to a LONG field. Original field will remain of the
BIT type and will be returned to a client.
@note setup_ref_array() needs to account for the extra space.
*/
Item_field *new_item= new Item_field(thd, (Item_field*)item);
ord->item= thd->lex->current_select()->add_hidden_item(new_item);
}
else
{
/*
We have here only field_list (not all_field_list), so we can use
simple indexing of ref_pointer_array (order in the array and in the
list are same)
*/
ord->item= &ref_pointer_array[0];
}
ord->direction= ORDER::ORDER_ASC;
*prev=ord;
prev= &ord->next;
}
next_item:
ref_pointer_array.pop_front();
}
*prev=0;
return group;
}
/**
Return table number if there is only one table in sort order
and group and order is compatible, else return 0.
*/
static TABLE *
get_sort_by_table(ORDER *a,ORDER *b,TABLE_LIST *tables)
{
table_map map= (table_map) 0;
DBUG_ENTER("get_sort_by_table");
if (!a)
a=b; // Only one need to be given
else if (!b)
b=a;
for (; a && b; a=a->next,b=b->next)
{
if (!(*a->item)->eq(*b->item,1))
DBUG_RETURN(0);
map|=a->item[0]->used_tables();
}
map&= ~PARAM_TABLE_BIT;
if (!map || (map & (RAND_TABLE_BIT | OUTER_REF_TABLE_BIT)))
DBUG_RETURN(0);
for (; !(map & tables->map()); tables= tables->next_leaf) ;
if (map != tables->map())
DBUG_RETURN(0); // More than one table
DBUG_PRINT("exit",("sort by table: %d",tables->tableno()));
DBUG_RETURN(tables->table);
}
/**
Create a condition for a const reference for a table.
@param thd THD pointer
@param join_tab pointer to the table
@return A pointer to the created condition for the const reference.
@retval !NULL if the condition was created successfully
@retval NULL if an error has occured
*/
static Item_cond_and *create_cond_for_const_ref(THD *thd, JOIN_TAB *join_tab)
{
DBUG_ENTER("create_cond_for_const_ref");
assert(join_tab->ref().key_parts);
TABLE *table= join_tab->table();
Item_cond_and *cond= new Item_cond_and();
if (!cond)
DBUG_RETURN(NULL);
for (uint i=0 ; i < join_tab->ref().key_parts ; i++)
{
Field *field= table->field[table->key_info[join_tab->ref().key].key_part[i].
fieldnr-1];
Item *value= join_tab->ref().items[i];
Item *item= new Item_field(field);
if (!item)
DBUG_RETURN(NULL);
item= join_tab->ref().null_rejecting & ((key_part_map)1 << i) ?
(Item *)new Item_func_eq(item, value) :
(Item *)new Item_func_equal(item, value);
if (!item)
DBUG_RETURN(NULL);
if (cond->add(item))
DBUG_RETURN(NULL);
}
cond->fix_fields(thd, (Item**)&cond);
DBUG_RETURN(cond);
}
/**
Create a condition for a const reference and add this to the
currenct select for the table.
*/
static bool add_ref_to_table_cond(THD *thd, JOIN_TAB *join_tab)
{
DBUG_ENTER("add_ref_to_table_cond");
if (!join_tab->ref().key_parts)
DBUG_RETURN(FALSE);
int error= 0;
/* Create a condition representing the const reference. */
Item_cond_and *cond= create_cond_for_const_ref(thd, join_tab);
if (!cond)
DBUG_RETURN(TRUE);
/* Add this condition to the existing select condtion */
if (join_tab->condition())
{
error=(int) cond->add(join_tab->condition());
cond->update_used_tables();
}
join_tab->set_condition(cond);
Opt_trace_object(&thd->opt_trace).add("added_back_ref_condition", cond);
DBUG_RETURN(error ? TRUE : FALSE);
}
/**
Remove additional condition inserted by IN/ALL/ANY transformation.
@param conds condition for processing
@return
new conditions
@note that this function has Bug#13915291.
*/
static Item *remove_additional_cond(Item* conds)
{
// Because it uses in_additional_cond it applies only to the scalar case.
if (conds->item_name.ptr() == in_additional_cond)
return 0;
if (conds->type() == Item::COND_ITEM)
{
Item_cond *cnd= (Item_cond*) conds;
List_iterator<Item> li(*(cnd->argument_list()));
Item *item;
while ((item= li++))
{
if (item->item_name.ptr() == in_additional_cond)
{
li.remove();
if (cnd->argument_list()->elements == 1)
return cnd->argument_list()->head();
return conds;
}
}
}
return conds;
}
/**
Update some values in keyuse for faster choose_table_order() loop.
@todo Check if this is the real meaning of ref_table_rows.
@param keyuse_array Array of Key_use elements being updated.
*/
void JOIN::optimize_keyuse()
{
for (size_t ix= 0; ix < keyuse_array.size(); ++ix)
{
Key_use *keyuse= &keyuse_array.at(ix);
table_map map;
/*
If we find a ref, assume this table matches a proportional
part of this table.
For example 100 records matching a table with 5000 records
gives 5000/100 = 50 records per key
Constant tables are ignored.
To avoid bad matches, we don't make ref_table_rows less than 100.
*/
keyuse->ref_table_rows= ~(ha_rows) 0; // If no ref
if (keyuse->used_tables &
(map= (keyuse->used_tables & ~const_table_map & ~PSEUDO_TABLE_BITS)))
{
uint tableno;
for (tableno= 0; ! (map & 1) ; map>>=1, tableno++)
{}
if (map == 1) // Only one table
{
TABLE *tmp_table= join_tab[tableno].table();
keyuse->ref_table_rows= max<ha_rows>(tmp_table->file->stats.records, 100);
}
}
/*
Outer reference (external field) is constant for single executing
of subquery
*/
if (keyuse->used_tables == OUTER_REF_TABLE_BIT)
keyuse->ref_table_rows= 1;
}
}
/**
Function sets FT hints, initializes FT handlers
and checks if FT index can be used as covered.
*/
bool JOIN::optimize_fts_query()
{
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
assert(select_lex->has_ft_funcs());
for (uint i= const_tables; i < tables; i++)
{
JOIN_TAB *tab= best_ref[i];
if (tab->type() != JT_FT)
continue;
Item_func_match *ifm;
Item_func_match* ft_func=
static_cast<Item_func_match*>(tab->position()->key->val);
List_iterator<Item_func_match> li(*(select_lex->ftfunc_list));
while ((ifm= li++))
{
if (!(ifm->used_tables() & tab->table_ref->map()) || ifm->master)
continue;
if (ifm != ft_func)
{
if (ifm->can_skip_ranking())
ifm->set_hints(this, FT_NO_RANKING, HA_POS_ERROR, false);
}
}
/*
Check if internal sorting is needed. FT_SORTED flag is set
if no ORDER BY clause or ORDER BY MATCH function is the same
as the function that is used for FT index and FT table is
the first non-constant table in the JOIN.
*/
if (i == const_tables &&
!(ft_func->get_hints()->get_flags() & FT_BOOL) &&
(!order || ft_func == test_if_ft_index_order(order)))
ft_func->set_hints(this, FT_SORTED, m_select_limit, false);
/*
Check if ranking is not needed. FT_NO_RANKING flag is set if
MATCH function is used only in WHERE condition and MATCH
function is not part of an expression.
*/
if (ft_func->can_skip_ranking())
ft_func->set_hints(this, FT_NO_RANKING,
!order ? m_select_limit : HA_POS_ERROR, false);
}
return init_ftfuncs(thd, select_lex);
}
/**
Check if FTS index only access is possible.
@param tab pointer to JOIN_TAB structure.
@return TRUE if index only access is possible,
FALSE otherwise.
*/
bool JOIN::fts_index_access(JOIN_TAB *tab)
{
assert(tab->type() == JT_FT);
TABLE *table= tab->table();
if ((table->file->ha_table_flags() & HA_CAN_FULLTEXT_EXT) == 0)
return false; // Optimizations requires extended FTS support by table engine
/*
This optimization does not work with filesort nor GROUP BY
*/
if (grouped || (order && ordered_index_usage != ordered_index_order_by))
return false;
/*
Check whether the FTS result is covering. If only document id
and rank is needed, there is no need to access table rows.
*/
for (uint i= bitmap_get_first_set(table->read_set);
i < table->s->fields;
i= bitmap_get_next_set(table->read_set, i))
{
if (table->field[i] != table->fts_doc_id_field ||
!tab->ft_func()->docid_in_result())
return false;
}
return true;
}
/**
For {semijoin,subquery} materialization: calculates various cost
information, based on a plan in join->best_positions covering the
to-be-materialized query block and only this.
@param join JOIN where plan can be found
@param sj_nest sj materialization nest (NULL if subquery materialization)
@param n_tables number of to-be-materialized tables
@param[out] sjm where computed costs will be stored
@note that this function modifies join->map2table, which has to be filled
correctly later.
*/
static void calculate_materialization_costs(JOIN *join,
TABLE_LIST *sj_nest,
uint n_tables,
Semijoin_mat_optimize *sjm)
{
double mat_cost; // Estimated cost of materialization
double mat_rowcount; // Estimated row count before duplicate removal
double distinct_rowcount; // Estimated rowcount after duplicate removal
List<Item> *inner_expr_list;
if (sj_nest)
{
/*
get_partial_join_cost() assumes a regular join, which is correct when
we optimize a sj-materialization nest (always executed as regular
join).
*/
get_partial_join_cost(join, n_tables, &mat_cost, &mat_rowcount);
n_tables+= join->const_tables;
inner_expr_list= &sj_nest->nested_join->sj_inner_exprs;
}
else
{
mat_cost= join->best_read;
mat_rowcount= static_cast<double>(join->best_rowcount);
inner_expr_list= &join->select_lex->item_list;
}
/*
Adjust output cardinality estimates. If the subquery has form
... oe IN (SELECT t1.colX, t2.colY, func(X,Y,Z) )
then the number of distinct output record combinations has an
upper bound of product of number of records matching the tables
that are used by the SELECT clause.
TODO:
We can get a more precise estimate if we
- use rec_per_key cardinality estimates. For simple cases like
"oe IN (SELECT t.key ...)" it is trivial.
- Functional dependencies between the tables in the semi-join
nest (the payoff is probably less here?)
*/
{
for (uint i=0 ; i < n_tables ; i++)
{
JOIN_TAB * const tab= join->best_positions[i].table;
join->map2table[tab->table_ref->tableno()]= tab;
}
List_iterator<Item> it(*inner_expr_list);
Item *item;
table_map map= 0;
while ((item= it++))
map|= item->used_tables();
map&= ~PSEUDO_TABLE_BITS;
Table_map_iterator tm_it(map);
int tableno;
double rows= 1.0;
while ((tableno = tm_it.next_bit()) != Table_map_iterator::BITMAP_END)
rows*= join->map2table[tableno]->table()->quick_condition_rows;
distinct_rowcount= min(mat_rowcount, rows);
}
/*
Calculate temporary table parameters and usage costs
*/
const uint rowlen= get_tmp_table_rec_length(*inner_expr_list);
const Cost_model_server *cost_model= join->cost_model();
Cost_model_server::enum_tmptable_type tmp_table_type;
if (rowlen * distinct_rowcount < join->thd->variables.max_heap_table_size)
tmp_table_type= Cost_model_server::MEMORY_TMPTABLE;
else
tmp_table_type= Cost_model_server::DISK_TMPTABLE;
/*
Let materialization cost include the cost to create the temporary
table and write the rows into it:
*/
mat_cost+= cost_model->tmptable_create_cost(tmp_table_type);
mat_cost+= cost_model->tmptable_readwrite_cost(tmp_table_type, mat_rowcount,
0.0);
sjm->materialization_cost.reset();
sjm->materialization_cost.add_io(mat_cost);
sjm->expected_rowcount= distinct_rowcount;
/*
Set the cost to do a full scan of the temptable (will need this to
consider doing sjm-scan):
*/
sjm->scan_cost.reset();
if (distinct_rowcount > 0.0)
{
const double scan_cost=
cost_model->tmptable_readwrite_cost(tmp_table_type,
0.0, distinct_rowcount);
sjm->scan_cost.add_io(scan_cost);
}
// The cost to lookup a row in temp. table
const double row_cost= cost_model->tmptable_readwrite_cost(tmp_table_type,
0.0, 1.0);
sjm->lookup_cost.reset();
sjm->lookup_cost.add_io(row_cost);
}
/**
Decides between EXISTS and materialization; performs last steps to set up
the chosen strategy.
@returns 'false' if no error
@note If UNION this is called on each contained JOIN.
*/
bool JOIN::decide_subquery_strategy()
{
assert(unit->item);
switch (unit->item->substype())
{
case Item_subselect::IN_SUBS:
case Item_subselect::ALL_SUBS:
case Item_subselect::ANY_SUBS:
// All of those are children of Item_in_subselect and may use EXISTS
break;
default:
return false;
}
Item_in_subselect * const in_pred=
static_cast<Item_in_subselect *>(unit->item);
Item_exists_subselect::enum_exec_method chosen_method= in_pred->exec_method;
// Materialization does not allow UNION so this can't happen:
assert(chosen_method != Item_exists_subselect::EXEC_MATERIALIZATION);
if ((chosen_method == Item_exists_subselect::EXEC_EXISTS_OR_MAT) &&
compare_costs_of_subquery_strategies(&chosen_method))
return true;
switch (chosen_method)
{
case Item_exists_subselect::EXEC_EXISTS:
return in_pred->finalize_exists_transform(select_lex);
case Item_exists_subselect::EXEC_MATERIALIZATION:
return in_pred->finalize_materialization_transform(this);
default:
assert(false);
return true;
}
}
/**
Tells what is the cheapest between IN->EXISTS and subquery materialization,
in terms of cost, for the subquery's JOIN.
Input:
- join->{best_positions,best_read,best_rowcount} must contain the
execution plan of EXISTS (where 'join' is the subquery's JOIN)
- join2->{best_positions,best_read,best_rowcount} must be correctly set
(where 'join2' is the parent join, the grandparent join, etc).
Output:
join->{best_positions,best_read,best_rowcount} contain the cheapest
execution plan (where 'join' is the subquery's JOIN).
This plan choice has to happen before calling functions which set up
execution structures, like JOIN::get_best_combination().
@param[out] method chosen method (EXISTS or materialization) will be put
here.
@returns false if success
*/
bool JOIN::compare_costs_of_subquery_strategies(
Item_exists_subselect::enum_exec_method *method)
{
*method= Item_exists_subselect::EXEC_EXISTS;
Item_exists_subselect::enum_exec_method allowed_strategies=
select_lex->subquery_strategy(thd);
if (allowed_strategies == Item_exists_subselect::EXEC_EXISTS)
return false;
assert(allowed_strategies == Item_exists_subselect::EXEC_EXISTS_OR_MAT ||
allowed_strategies == Item_exists_subselect::EXEC_MATERIALIZATION);
const JOIN *parent_join= unit->outer_select()->join;
if (!parent_join || !parent_join->child_subquery_can_materialize)
return false;
Item_in_subselect * const in_pred=
static_cast<Item_in_subselect *>(unit->item);
/*
Testing subquery_allows_etc() at each optimization is necessary as each
execution of a prepared statement may use a different type of parameter.
*/
if (!subquery_allows_materialization(in_pred, thd, select_lex,
select_lex->outer_select()))
return false;
Opt_trace_context * const trace= &thd->opt_trace;
Opt_trace_object trace_wrapper(trace);
Opt_trace_object
trace_subqmat(trace, "execution_plan_for_potential_materialization");
const double saved_best_read= best_read;
const ha_rows saved_best_rowcount= best_rowcount;
POSITION * const saved_best_pos= best_positions;
if (in_pred->in2exists_added_to_where())
{
Opt_trace_array trace_subqmat_steps(trace, "steps");
// Up to one extra slot per semi-join nest is needed (if materialized)
const uint sj_nests= select_lex->sj_nests.elements;
if (!(best_positions= new (thd->mem_root) POSITION[tables + sj_nests]))
return true;
// Compute plans which do not use outer references
assert(allow_outer_refs);
allow_outer_refs= false;
if (optimize_semijoin_nests_for_materialization(this))
return true;
if (Optimize_table_order(thd, this, NULL).choose_table_order())
return true;
}
else
{
/*
If IN->EXISTS didn't add any condition to WHERE (only to HAVING, which
can happen if subquery has aggregates) then the plan for materialization
will be the same as for EXISTS - don't compute it again.
*/
trace_subqmat.add("surely_same_plan_as_EXISTS", true).
add_alnum("cause", "EXISTS_did_not_change_WHERE");
}
Semijoin_mat_optimize sjm;
calculate_materialization_costs(this, NULL, primary_tables, &sjm);
/*
The number of evaluations of the subquery influences costs, we need to
compute it.
*/
Opt_trace_object trace_subq_mat_decision(trace, "subq_mat_decision");
Opt_trace_array trace_parents(trace, "parent_fanouts");
const Item_subselect *subs= in_pred;
double subq_executions= 1.0;
for(;;)
{
Opt_trace_object trace_parent(trace);
trace_parent.add_select_number(parent_join->select_lex->select_number);
double parent_fanout;
if (// safety, not sure needed
parent_join->plan_is_const() ||
// if subq is in condition on constant table:
!parent_join->child_subquery_can_materialize)
{
parent_fanout= 1.0;
trace_parent.add("subq_attached_to_const_table", true);
}
else
{
if (subs->in_cond_of_tab != NO_PLAN_IDX)
{
/*
Subquery is attached to a certain 'pos', pos[-1].prefix_rowcount
is the number of times we'll start a loop accessing 'pos'; each such
loop will read pos->rows_fetched rows of 'pos', so subquery will
be evaluated pos[-1].prefix_rowcount * pos->rows_fetched times.
Exceptions:
- if 'pos' is first, use 1.0 instead of pos[-1].prefix_rowcount
- if 'pos' is first of a sj-materialization nest, same.
If in a sj-materialization nest, pos->rows_fetched and
pos[-1].prefix_rowcount are of the "nest materialization" plan
(copied back in fix_semijoin_strategies()), which is
appropriate as it corresponds to evaluations of our subquery.
pos->prefix_rowcount is not suitable because if we have:
select ... from ot1 where ot1.col in
(select it1.col1 from it1 where it1.col2 not in (subq));
and subq does subq-mat, and plan is ot1 - it1+firstmatch(ot1),
then:
- t1.prefix_rowcount==1 (due to firstmatch)
- subq is attached to it1, and is evaluated for each row read from
t1, potentially way more than 1.
*/
const uint idx= subs->in_cond_of_tab;
assert((int)idx >= 0 && idx < parent_join->tables);
trace_parent.add("subq_attached_to_table", true);
QEP_TAB *const parent_tab= &parent_join->qep_tab[idx];
trace_parent.add_utf8_table(parent_tab->table_ref);
parent_fanout= parent_tab->position()->rows_fetched;
if ((idx > parent_join->const_tables) &&
!sj_is_materialize_strategy(parent_tab->position()->sj_strategy))
parent_fanout*=
parent_tab[-1].position()->prefix_rowcount;
}
else
{
/*
Subquery is SELECT list, GROUP BY, ORDER BY, HAVING: it is evaluated
at the end of the parent join's execution.
It can be evaluated once per row-before-grouping:
SELECT SUM(t1.col IN (subq)) FROM t1 GROUP BY expr;
or once per row-after-grouping:
SELECT SUM(t1.col) AS s FROM t1 GROUP BY expr HAVING s IN (subq),
SELECT SUM(t1.col) IN (subq) FROM t1 GROUP BY expr
It's hard to tell. We simply assume 'once per
row-before-grouping'.
Another approximation:
SELECT ... HAVING x IN (subq) LIMIT 1
best_rowcount=1 due to LIMIT, though HAVING (and thus the subquery)
may be evaluated many times before HAVING becomes true and the limit
is reached.
*/
trace_parent.add("subq_attached_to_join_result", true);
parent_fanout= static_cast<double>(parent_join->best_rowcount);
}
}
subq_executions*= parent_fanout;
trace_parent.add("fanout", parent_fanout);
const bool cacheable= parent_join->select_lex->is_cacheable();
trace_parent.add("cacheable", cacheable);
if (cacheable)
{
// Parent executed only once
break;
}
/*
Parent query is executed once per outer row => go up to find number of
outer rows. Example:
SELECT ... IN(subq-with-in2exists WHERE ... IN (subq-with-mat))
*/
if (!(subs= parent_join->unit->item))
{
// derived table, materialized only once
break;
}
parent_join= parent_join->unit->outer_select()->join;
if (!parent_join)
{
/*
May be single-table UPDATE/DELETE, has no join.
@todo we should find how many rows it plans to UPDATE/DELETE, taking
inspiration in Explain_table::explain_rows_and_filtered().
This is not a priority as it applies only to
UPDATE - child(non-mat-subq) - grandchild(may-be-mat-subq).
And it will autosolve the day UPDATE gets a JOIN.
*/
break;
}
} // for(;;)
trace_parents.end();
const double cost_exists= subq_executions * saved_best_read;
const double cost_mat_table= sjm.materialization_cost.total_cost();
const double cost_mat= cost_mat_table + subq_executions *
sjm.lookup_cost.total_cost();
const bool mat_chosen=
(allowed_strategies == Item_exists_subselect::EXEC_EXISTS_OR_MAT) ?
(cost_mat < cost_exists) : true;
trace_subq_mat_decision
.add("cost_to_create_and_fill_materialized_table",
cost_mat_table)
.add("cost_of_one_EXISTS", saved_best_read)
.add("number_of_subquery_evaluations", subq_executions)
.add("cost_of_materialization", cost_mat)
.add("cost_of_EXISTS", cost_exists)
.add("chosen", mat_chosen);
if (mat_chosen)
*method= Item_exists_subselect::EXEC_MATERIALIZATION;
else
{
best_read= saved_best_read;
best_rowcount= saved_best_rowcount;
best_positions= saved_best_pos;
/*
Don't restore JOIN::positions or best_ref, they're not used
afterwards. best_positions is (like: by get_sj_strategy()).
*/
}
return false;
}
/**
Optimize rollup specification.
Allocate objects needed for rollup processing.
@returns false if success, true if error.
*/
bool JOIN::optimize_rollup()
{
tmp_table_param.quick_group= 0; // Can't create groups in tmp table
rollup.state= ROLLUP::STATE_INITED;
/*
Create pointers to the different sum function groups
These are updated by rollup_make_fields()
*/
tmp_table_param.group_parts= send_group_parts;
/*
substitute_gc() might substitute an expression in the GROUP BY list with
a generated column. In such case the GC is added to the all_fields as a
hidden field. In total, all_fields list could be grown by up to
send_group_parts columns. Reserve space for them here.
*/
const uint ref_array_size= all_fields.elements + send_group_parts;
Item_null_result **null_items=
static_cast<Item_null_result**>(thd->alloc(sizeof(Item*)*send_group_parts));
rollup.null_items= Item_null_array(null_items, send_group_parts);
rollup.ref_pointer_arrays=
static_cast<Ref_ptr_array*>
(thd->alloc((sizeof(Ref_ptr_array) +
ref_array_size * sizeof(Item*)) * send_group_parts));
rollup.fields=
static_cast<List<Item>*>(thd->alloc(sizeof(List<Item>) * send_group_parts));
if (!null_items || !rollup.ref_pointer_arrays || !rollup.fields)
return true;
Item **ref_array= (Item**) (rollup.ref_pointer_arrays+send_group_parts);
/*
Prepare space for field list for the different levels
These will be filled up in rollup_make_fields()
*/
ORDER *group= group_list;
for (uint i= 0; i < send_group_parts; i++, group= group->next)
{
rollup.null_items[i]=
new (thd->mem_root) Item_null_result((*group->item)->field_type(),
(*group->item)->result_type());
if (rollup.null_items[i] == NULL)
return true; /* purecov: inspected */
List<Item> *rollup_fields= &rollup.fields[i];
rollup_fields->empty();
rollup.ref_pointer_arrays[i]= Ref_ptr_array(ref_array, ref_array_size);
ref_array+= ref_array_size;
}
for (uint i= 0; i < send_group_parts; i++)
{
for (uint j= 0; j < fields_list.elements; j++)
rollup.fields[i].push_back(rollup.null_items[i]);
}
return false;
}
/**
Refine the best_rowcount estimation based on what happens after tables
have been joined: LIMIT and type of result sink.
*/
void JOIN::refine_best_rowcount()
{
// If plan is const, 0 or 1 rows should be returned
assert(!plan_is_const() || best_rowcount <= 1);
if (plan_is_const())
return;
/*
If a derived table, or a member of a UNION which itself forms a derived
table:
setting estimate to 0 or 1 row would mark the derived table as const.
The row count is bumped to the nearest higher value, so that the
query block will not be evaluated during optimization.
*/
if (best_rowcount <= 1 &&
select_lex->master_unit()->first_select()->linkage ==
DERIVED_TABLE_TYPE)
best_rowcount= 2;
/*
There will be no more rows than defined in the LIMIT clause. Use it
as an estimate. If LIMIT 1 is specified, the query block will be
considered "const", with actual row count 0 or 1.
*/
set_if_smaller(best_rowcount, unit->select_limit_cnt);
}
/**
@} (end of group Query_Optimizer)
*/
/**
This function is used to get the key length of Item object on
which one tmp field will be created during create_tmp_table.
This function references KEY_PART_INFO::init_from_field().
@param item A inner item of outer join
@return The length of a item to be as a key of a temp table
*/
static uint32 get_key_length_tmp_table(Item *item)
{
uint32 len= 0;
item= item->real_item();
if (item->type() == Item::FIELD_ITEM)
len= ((Item_field *)item)->field->key_length();
else
len= item->max_length;
if (item->maybe_null)
len+= HA_KEY_NULL_LENGTH;
// references KEY_PART_INFO::init_from_field()
enum_field_types type= item->field_type();
if (type == MYSQL_TYPE_BLOB ||
type == MYSQL_TYPE_VARCHAR ||
type == MYSQL_TYPE_GEOMETRY)
len+= HA_KEY_BLOB_LENGTH;
return len;
}