drop table if exists t1;
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, primary key (a,a,a,a,a,a,a,a,a,a));
insert into t1 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, primary key (a,a,a,a,a,a,a,a,a,a));
insert into t1 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 (
bool     char(0) default NULL,
not_null varchar(20) binary NOT NULL default '',
misc     integer not null,
PRIMARY KEY  (not_null)
) TYPE=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;