drop table if exists t1,t2,t3,t11,t12; CREATE TABLE t1 (a tinyint(3), b tinyint(5)); INSERT INTO t1 VALUES (1,1); INSERT LOW_PRIORITY INTO t1 VALUES (1,2); INSERT INTO t1 VALUES (1,3); DELETE from t1 where a=1 limit 1; DELETE LOW_PRIORITY from t1 where a=1; INSERT INTO t1 VALUES (1,1); DELETE from t1; LOCK TABLE t1 write; INSERT INTO t1 VALUES (1,2); DELETE from t1; UNLOCK TABLES; INSERT INTO t1 VALUES (1,2); SET AUTOCOMMIT=0; DELETE from t1; SET AUTOCOMMIT=1; drop table t1; create table t1 ( a bigint not null, b bigint not null default 0, c bigint not null default 0, d bigint not null default 0, e bigint not null default 0, f bigint not null default 0, g bigint not null default 0, h bigint not null default 0, i bigint not null default 0, j bigint not null default 0, primary key (a,b,c,d,e,f,g,h,i,j)); insert into t1 (a) values (2),(4),(6),(8),(10),(12),(14),(16),(18),(20),(22),(24),(26),(23); delete from t1 where a=26; drop table t1; create table t1 ( a bigint not null, b bigint not null default 0, c bigint not null default 0, d bigint not null default 0, e bigint not null default 0, f bigint not null default 0, g bigint not null default 0, h bigint not null default 0, i bigint not null default 0, j bigint not null default 0, primary key (a,b,c,d,e,f,g,h,i,j)); insert into t1 (a) values (2),(4),(6),(8),(10),(12),(14),(16),(18),(20),(22),(24),(26),(23),(27); delete from t1 where a=27; drop table t1; CREATE TABLE `t1` ( `i` int(10) NOT NULL default '0', `i2` int(10) NOT NULL default '0', PRIMARY KEY (`i`) ); DELETE FROM t1 USING t1 WHERE post='1'; ERROR 42S22: Unknown column 'post' in 'where clause' drop table t1; CREATE TABLE t1 ( bool char(0) default NULL, not_null varchar(20) binary NOT NULL default '', misc integer not null, PRIMARY KEY (not_null) ) ENGINE=MyISAM; INSERT INTO t1 VALUES (NULL,'a',4), (NULL,'b',5), (NULL,'c',6), (NULL,'d',7); select * from t1 where misc > 5 and bool is null; bool not_null misc NULL c 6 NULL d 7 delete from t1 where misc > 5 and bool is null; select * from t1 where misc > 5 and bool is null; bool not_null misc select count(*) from t1; count(*) 2 delete from t1 where 1 > 2; select count(*) from t1; count(*) 2 delete from t1 where 3 > 2; select count(*) from t1; count(*) 0 drop table t1; create table t1 (a int not null auto_increment primary key, b char(32)); insert into t1 (b) values ('apple'), ('apple'); select * from t1; a b 1 apple 2 apple delete t1 from t1, t1 as t2 where t1.b = t2.b and t1.a > t2.a; select * from t1; a b 1 apple drop table t1; create table t11 (a int NOT NULL, b int, primary key (a)); create table t12 (a int NOT NULL, b int, primary key (a)); create table t2 (a int NOT NULL, b int, primary key (a)); insert into t11 values (0, 10),(1, 11),(2, 12); insert into t12 values (33, 10),(0, 11),(2, 12); insert into t2 values (1, 21),(2, 12),(3, 23); select * from t11; a b 0 10 1 11 2 12 select * from t12; a b 33 10 0 11 2 12 select * from t2; a b 1 21 2 12 3 23 delete t11.*, t12.* from t11,t12 where t11.a = t12.a and t11.b <> (select b from t2 where t11.a < t2.a); ERROR 21000: Subquery returns more than 1 row select * from t11; a b 0 10 1 11 2 12 select * from t12; a b 33 10 0 11 2 12 delete ignore t11.*, t12.* from t11,t12 where t11.a = t12.a and t11.b <> (select b from t2 where t11.a < t2.a); Warnings: Error 1242 Subquery returns more than 1 row Error 1242 Subquery returns more than 1 row select * from t11; a b 0 10 1 11 select * from t12; a b 33 10 0 11 insert into t11 values (2, 12); delete from t11 where t11.b <> (select b from t2 where t11.a < t2.a); ERROR 21000: Subquery returns more than 1 row select * from t11; a b 0 10 1 11 2 12 delete ignore from t11 where t11.b <> (select b from t2 where t11.a < t2.a); Warnings: Error 1242 Subquery returns more than 1 row Error 1242 Subquery returns more than 1 row select * from t11; a b 0 10 1 11 drop table t11, t12, t2; create table t1 (a int, b int, unique key (a), key (b)); insert into t1 values (3, 3), (7, 7); delete t1 from t1 where a = 3; check table t1; Table Op Msg_type Msg_text test.t1 check status OK select * from t1; a b 7 7 drop table t1; CREATE TABLE t1 ( a int PRIMARY KEY ); DELETE FROM t1 WHERE t1.a > 0 ORDER BY t1.a; INSERT INTO t1 VALUES (0),(1),(2); DELETE FROM t1 WHERE t1.a > 0 ORDER BY t1.a LIMIT 1; SELECT * FROM t1; a 0 2 DROP TABLE t1; create table t1 (a int); delete `4.t1` from t1 as `4.t1` where `4.t1`.a = 5; delete FROM `4.t1` USING t1 as `4.t1` where `4.t1`.a = 5; drop table t1; CREATE TABLE t1 (a int not null,b int not null); CREATE TABLE t2 (a int not null, b int not null, primary key (a,b)); CREATE TABLE t3 (a int not null, b int not null, primary key (a,b)); insert into t1 values (1,1),(2,1),(1,3); insert into t2 values (1,1),(2,2),(3,3); insert into t3 values (1,1),(2,1),(1,3); select * from t1,t2,t3 where t1.a=t2.a AND t2.b=t3.a and t1.b=t3.b; a b a b a b 1 1 1 1 1 1 2 1 2 2 2 1 1 3 1 1 1 3 explain select * from t1,t2,t3 where t1.a=t2.a AND t2.b=t3.a and t1.b=t3.b; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 3 1 SIMPLE t2 ref PRIMARY PRIMARY 4 test.t1.a 1 Using index 1 SIMPLE t3 eq_ref PRIMARY PRIMARY 8 test.t2.b,test.t1.b 1 Using index delete t2.*,t3.* from t1,t2,t3 where t1.a=t2.a AND t2.b=t3.a and t1.b=t3.b; select * from t3; a b drop table t1,t2,t3; create table t1(a date not null); insert into t1 values (0); select * from t1 where a is null; a 0000-00-00 delete from t1 where a is null; select count(*) from t1; count(*) 0 drop table t1;