Mysql的语句：用select来update

从 t2表中 select 出来数据 ，更新 t1 表里面的数据。

update t1

set

t1.count = (

select max(num) from t2 where t1.id = t2.pid group by pid

) 

update t1 set t1.count = (select max(num) from t2 where t1.id = t2.pid group by pid ) 

在用来更新一些 统计数据方面很有用。

还有

insert into with select insert into myDestTable (userid, name, value, othercolumns) select us.userid, us.name,'myvaluefromcode', othercolumns from users us where us.name = 'mynamefromcode'

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