MySQL 各种级联查询后更新（update select）.
CREATE TABLE `tb1` (
`id` int(11) NOT NULL,
`A` varchar(100) default NULL,
`B` varchar(100) default NULL,
`C` varchar(20) default NULL,
PRIMARY KEY (`id`),
KEY `id` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE `tb2` (
`id` int(11) NOT NULL,
`A` varchar(100) default NULL,
`B` varchar(100) default NULL,
PRIMARY KEY (`id`),
KEY `id` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
级联更新1：
update tb1,
tb2
set tb1.a=tb2.a,tb1.b=tb2.b
where tb1.id=tb2.id
级联更新2：
update tb1,
(select * from tb2) as tb2
set tb1.a=tb2.a,tb1.b=tb2.b
where tb1.id=tb2.id
级联更新3：
update (select * from tb1 group by C) as temp,
tb2,
tb1
set tb1.a = tb2.a,
tb1.b = tb2.b
where tb1.id = tb2.id and
temp.id = tb2.id
级联更新4：
update tb1 left join tb2 on tb1.id = tb2.id
set tb1.a = tb2.a,
tb1.b = tb2.b
where ......