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DROP TABLE IF EXISTS t1; CREATE TABLE t1 (a INT AUTO_INCREMENT PRIMARY KEY, b CHAR(20) ); SET @start_value= @@global.max_seeks_for_key; '#--------------------FN_DYNVARS_084_01-------------------------#' SELECT @@global.max_seeks_for_key = 10; @@global.max_seeks_for_key = 10 0 SELECT @@session.max_seeks_for_key = 10; @@session.max_seeks_for_key = 10 0 SET @@global.max_seeks_for_key = 20; SELECT @@global.max_seeks_for_key; @@global.max_seeks_for_key 20 INSERT INTO t1(b) VALUES("AREc"); EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b; id select_type table partitions type possible_keys key key_len ref rows filtered Extra 1 SIMPLE t1 NULL ALL NULL NULL NULL NULL # # NULL 1 SIMPLE t2 NULL ALL NULL NULL NULL NULL # # Using where; Using join buffer (Block Nested Loop) Warnings: Note 1003 /* select#1 */ select straight_join `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t1` join `test`.`t1` `t2` where (`test`.`t2`.`b` = `test`.`t1`.`b`) SET @@session.max_seeks_for_key = 2; SELECT @@session.max_seeks_for_key; @@session.max_seeks_for_key 2 INSERT INTO t1(b) VALUES("BREc"); INSERT INTO t1(b) VALUES("CRec"); EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b; id select_type table partitions type possible_keys key key_len ref rows filtered Extra 1 SIMPLE t1 NULL ALL NULL NULL NULL NULL # # NULL 1 SIMPLE t2 NULL ALL NULL NULL NULL NULL # # Using where; Using join buffer (Block Nested Loop) Warnings: Note 1003 /* select#1 */ select straight_join `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t1` join `test`.`t1` `t2` where (`test`.`t2`.`b` = `test`.`t1`.`b`) '#--------------------FN_DYNVARS_084_02-------------------------#' SELECT @@global.max_seeks_for_key = 10; @@global.max_seeks_for_key = 10 0 SELECT @@session.max_seeks_for_key = 10; @@session.max_seeks_for_key = 10 0 SET @@global.max_seeks_for_key = 20; SELECT @@global.max_seeks_for_key; @@global.max_seeks_for_key 20 INSERT INTO t1(b) VALUES("AREc"); EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b; id select_type table partitions type possible_keys key key_len ref rows filtered Extra 1 SIMPLE t1 NULL ALL NULL NULL NULL NULL # # NULL 1 SIMPLE t2 NULL ALL NULL NULL NULL NULL # # Using where; Using join buffer (Block Nested Loop) Warnings: Note 1003 /* select#1 */ select straight_join `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t1` join `test`.`t1` `t2` where (`test`.`t2`.`b` = `test`.`t1`.`b`) SET @@session.max_seeks_for_key = 2; SELECT @@session.max_seeks_for_key; @@session.max_seeks_for_key 2 INSERT INTO t1(b) VALUES("BREc"); INSERT INTO t1(b) VALUES("CRec"); EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b; id select_type table partitions type possible_keys key key_len ref rows filtered Extra 1 SIMPLE t1 NULL ALL NULL NULL NULL NULL # # NULL 1 SIMPLE t2 NULL ALL NULL NULL NULL NULL # # Using where; Using join buffer (Block Nested Loop) Warnings: Note 1003 /* select#1 */ select straight_join `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t1` join `test`.`t1` `t2` where (`test`.`t2`.`b` = `test`.`t1`.`b`) INSERT INTO t1 VALUES(null,"test"); INSERT INTO t1 VALUES (null,"a"),(null,"a"),(null,"a"), (null,"a"),(null,"a"),(null,"a"),(null,"a"), (null,"a"),(null,"a"),(null,"a"); EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b; id select_type table partitions type possible_keys key key_len ref rows filtered Extra 1 SIMPLE t1 NULL ALL NULL NULL NULL NULL # # NULL 1 SIMPLE t2 NULL ALL NULL NULL NULL NULL # # Using where; Using join buffer (Block Nested Loop) Warnings: Note 1003 /* select#1 */ select straight_join `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t1` join `test`.`t1` `t2` where (`test`.`t2`.`b` = `test`.`t1`.`b`) ANALYZE TABLE t1; Table Op Msg_type Msg_text test.t1 analyze status OK SET MAX_SEEKS_FOR_KEY=1; EXPLAIN SELECT STRAIGHT_JOIN * FROM t1,t1 AS t2 WHERE t1.b = t2.b; id select_type table partitions type possible_keys key key_len ref rows filtered Extra 1 SIMPLE t1 NULL ALL NULL NULL NULL NULL # # NULL 1 SIMPLE t2 NULL ALL NULL NULL NULL NULL # # Using where; Using join buffer (Block Nested Loop) Warnings: Note 1003 /* select#1 */ select straight_join `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t1` join `test`.`t1` `t2` where (`test`.`t2`.`b` = `test`.`t1`.`b`) SET MAX_SEEKS_FOR_KEY=DEFAULT; DROP TABLE t1; SET @@global.max_seeks_for_key= @start_value;