drop table if exists t1; create table t1 (a int primary key, b int not null); insert into t1 () values (); insert into t1 values (1,1),(2,1),(3,1); update t1 set a=4 where b=1 limit 1; select * from t1; a b 0 0 4 1 2 1 3 1 update t1 set b=2 where b=1 limit 2; select * from t1; a b 0 0 4 2 2 2 3 1 update t1 set b=4 where b=1; select * from t1; a b 0 0 4 2 2 2 3 4 delete from t1 where b=2 limit 1; select * from t1; a b 0 0 2 2 3 4 delete from t1 limit 1; select * from t1; a b 2 2 3 4 drop table t1; create table t1 (i int); insert into t1 (i) values(1),(1),(1); delete from t1 limit 1; update t1 set i=2 limit 1; delete from t1 limit 0; update t1 set i=3 limit 0; select * from t1; i 2 1 drop table t1; select 0 limit 0; 0 CREATE TABLE t1(id int auto_increment primary key, id2 int, index(id2)); INSERT INTO t1 (id2) values (0),(0),(0); DELETE FROM t1 WHERE id=1; INSERT INTO t1 SET id2=0; SELECT * FROM t1; id id2 4 0 2 0 3 0 DELETE FROM t1 WHERE id2 = 0 ORDER BY id LIMIT 1; SELECT * FROM t1; id id2 4 0 3 0 DELETE FROM t1 WHERE id2 = 0 ORDER BY id desc LIMIT 1; SELECT * FROM t1; id id2 3 0 DROP TABLE t1; create table t1 (a integer); insert into t1 values (1); select 1 as a from t1 union all select 1 from dual limit 1; a 1 (select 1 as a from t1) union all (select 1 from dual) limit 1; a 1 drop table t1;