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SET foreign_key_checks=0;
CREATE TABLE t1 (id int primary key, foreign key (id) references t2(id)) ENGINE=engine;
CREATE TABLE t2 (id int primary key, foreign key (id) references t1(id)) ENGINE=engine;
SET foreign_key_checks=1;
SELECT COUNT(*) FROM information_schema.key_column_usage
WHERE REFERENCED_TABLE_NAME in ('t1', 't2');
COUNT(*)
2
SET foreign_key_checks=0;
DROP TABLE t1, t2;
SET foreign_key_checks=0;
CREATE TABLE t1 (id int primary key, foreign key (id) references t2(id)) ENGINE=engine;
CREATE TABLE t2 (id int primary key, foreign key (id) references t1(id)) ENGINE=engine;
SET foreign_key_checks=1;
SELECT COUNT(*) FROM information_schema.key_column_usage
WHERE REFERENCED_TABLE_NAME in ('t1', 't2');
COUNT(*)
2
SET foreign_key_checks=0;
DROP TABLE t2, t1;
SET foreign_key_checks=1;
SET foreign_key_checks=0;
CREATE TABLE t1 (id int primary key, foreign key (id) references no_such_db.t2(id)) ENGINE=engine;
drop table t1;
SET foreign_key_checks=1;
create table t1(pk1 int primary key auto_increment,
a int,
b int
) engine=engine;
create table t2(pk2 int primary key auto_increment,
c int not null,
unique(c),
d int not null,
unique(d)
) engine=engine;
alter table t1
add constraint fk3 foreign key (a) references t2(c),
add constraint fk3 foreign key (b) references t2(d);
ERROR 42000: Duplicate key name 'fk3'
SET foreign_key_checks=0;
alter table t1
add constraint fk3 foreign key (a) references t2(c),
add constraint fk3 foreign key (b) references t2(d);
ERROR 42000: Duplicate key name 'fk3'
SET foreign_key_checks=1;
drop table t1, t2;
create table t2 (
pk2 int not null primary key,
c int
) engine=engine;
create table t1 (
pk1 int not null primary key,
b int,
foreign key (b) references t2(pk2)
) engine=engine;
truncate table t2;
ERROR 42000: Cannot truncate a table referenced in a foreign key constraint (<fk_def>)
set foreign_key_checks=1;
truncate table t2;
ERROR 42000: Cannot truncate a table referenced in a foreign key constraint (<fk_def>)
set foreign_key_checks=0;
drop table t1, t2;
create table t2 (
pk2 int not null primary key,
c int
) engine=engine;
create table t1 (
pk1 int not null primary key,
b int,
foreign key (b) references t2(pk2)
) engine=engine;
truncate table t1;
set foreign_key_checks=1;
truncate table t1;
set foreign_key_checks=0;
drop table t1, t2;
create table t1 (
a1 int primary key,
b1 int not null,
c1 int not null,
key (b1,c1)
) engine engine;
create table t2 (
a2 int primary key auto_increment,
b2 int not null,
c2 int not null
) engine engine;
alter table t2
add constraint foreign key fk1 (b2,c2) references t1 (c1,b1);
ERROR HY000: Failed to add the foreign key constaint. Missing index for constraint 'fk1' in the referenced table 't1'
insert into t1 (a1,b1,c1) values
(1,11,12),(2,21,22),(3,31,32);
insert into t2 (b2,c2)
select c1, b1 from t1;
drop table t2,t1;