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'