drop table if exists t1,t2,t3; create table t1(id1 int not null auto_increment primary key, t char(12)); create table t2(id2 int not null, t char(12)); create table t3(id3 int not null, t char(12), index(id3)); select count(*) from t1 where id1 > 95; count(*) 5 select count(*) from t2 where id2 > 95; count(*) 25 select count(*) from t3 where id3 > 95; count(*) 250 update t1,t2,t3 set t1.t="aaa", t2.t="bbb", t3.t="cc" where t1.id1 = t2.id2 and t2.id2 = t3.id3 and t1.id1 > 90; select count(*) from t1 where t = "aaa"; count(*) 10 select count(*) from t1 where id1 > 90; count(*) 10 select count(*) from t2 where t = "bbb"; count(*) 10 select count(*) from t2 where id2 > 90; count(*) 50 select count(*) from t3 where t = "cc"; count(*) 500 select count(*) from t3 where id3 > 90; count(*) 500 delete t1.*, t2.*, t3.* from t1,t2,t3 where t1.id1 = t2.id2 and t2.id2 = t3.id3 and t1.id1 > 95; check table t1, t2, t3; Table Op Msg_type Msg_text test.t1 check status OK test.t2 check status OK test.t3 check status OK select count(*) from t1 where id1 > 95; count(*) 0 select count(*) from t2 where id2 > 95; count(*) 0 select count(*) from t3 where id3 > 95; count(*) 0 delete t1, t2, t3 from t1,t2,t3 where t1.id1 = t2.id2 and t2.id2 = t3.id3 and t1.id1 > 5; select count(*) from t1 where id1 > 5; count(*) 0 select count(*) from t2 where id2 > 5; count(*) 0 select count(*) from t3 where id3 > 5; count(*) 0 delete from t1, t2, t3 using t1,t2,t3 where t1.id1 = t2.id2 and t2.id2 = t3.id3 and t1.id1 > 0; select count(*) from t1 where id1; count(*) 0 select count(*) from t2 where id2; count(*) 0 select count(*) from t3 where id3; count(*) 0 drop table t1,t2,t3; create table t1(id1 int not null primary key, t varchar(100)) pack_keys = 1; create table t2(id2 int not null, t varchar(100), index(id2)) pack_keys = 1; delete t1 from t1,t2 where t1.id1 = t2.id2 and t1.id1 > 500; drop table t1,t2; DROP TABLE IF EXISTS a,b,c; CREATE TABLE a ( id int(11) NOT NULL default '0', name varchar(10) default NULL, PRIMARY KEY (id) ) TYPE=MyISAM; INSERT INTO a VALUES (1,'aaa'),(2,'aaa'),(3,'aaa'); CREATE TABLE b ( id int(11) NOT NULL default '0', name varchar(10) default NULL, PRIMARY KEY (id) ) TYPE=MyISAM; INSERT INTO b VALUES (2,'bbb'),(3,'bbb'),(4,'bbb'); CREATE TABLE c ( id int(11) NOT NULL default '0', mydate datetime default NULL, PRIMARY KEY (id) ) TYPE=MyISAM; INSERT INTO c VALUES (1,'2002-02-04 00:00:00'),(3,'2002-05-12 00:00:00'),(5,'2002-05-12 00:00:00'),(6,'2002-06-22 00:00:00'),(7,'2002-07-22 00:00:00'); delete a,b,c from a,b,c where to_days(now())-to_days(c.mydate)>=30 and c.id=a.id and c.id=b.id; select * from c; id mydate 1 2002-02-04 00:00:00 5 2002-05-12 00:00:00 6 2002-06-22 00:00:00 7 2002-07-22 00:00:00 DROP TABLE IF EXISTS a,b,c; drop table if exists parent, child; CREATE TABLE IF NOT EXISTS `parent` ( `id` int(11) NOT NULL auto_increment, `tst` text, `tst1` text, PRIMARY KEY (`id`) ) TYPE=MyISAM; CREATE TABLE IF NOT EXISTS `child` ( `ID` int(11) NOT NULL auto_increment, `ParId` int(11) default NULL, `tst` text, `tst1` text, PRIMARY KEY (`ID`), KEY `IX_ParId_child` (`ParId`), FOREIGN KEY (`ParId`) REFERENCES `test.parent` (`id`) ) TYPE=MyISAM; INSERT INTO parent(tst,tst1) VALUES("MySQL","MySQL AB"), ("MSSQL","Microsoft"), ("ORACLE","ORACLE"); INSERT INTO child(ParId) VALUES(1), (2), (3); select * from child; ID ParId tst tst1 1 1 NULL NULL 2 2 NULL NULL 3 3 NULL NULL UPDATE child, parent SET child.tst = parent.tst, child.tst1 = parent.tst1 WHERE child.ParId = parent.Id; select * from child; ID ParId tst tst1 1 1 MySQL MySQL AB 2 2 MSSQL Microsoft 3 3 ORACLE ORACLE drop table parent, child;