MySQL中You can't specify target table for update in FROM clause错误的意思是说,不能先select出同一表中的某些值,再update这个表(在同一语句中)。 例如下面这个sql:
delete from tbl where id in ( select max(id) from tbl a where EXISTS ( select 1 from tbl b where a.tac=b.tac group by tac HAVING count(1)>1 ) group by tac )
改写成下面就行了:
delete from tbl where id in ( select a.id from ( select max(id) id from tbl a where EXISTS ( select 1 from tbl b where a.tac=b.tac group by tac HAVING count(1)>1 ) group by tac ) a )
也就是说将select出的结果再通过中间表select一遍,这样就规避了错误。注意,这个问题只出现于mysql,mssql和Oracle不会出现此问题。
You can't specify target table for update in FROM clause含义:不能在同一表中查询的数据作为同一表的更新数据。
例如:
我想查询t_user_asset的余额加上50000作为更新字段f_cashAmount的值,这样写是不行的。
- UPDATE t_user_asset SET f_cashAmount =
- (
- SELECT (ua.f_cashAmount+50000) cashAmount FROM t_user_asset ua WHERE ua.f_userId = 290
- )
- WHERE f_userId = 290
- UPDATE t_user_asset SET f_cashAmount =
- (
- SELECT ub.cashAmount FROM
- (
- SELECT (ua.f_cashAmount+50000) cashAmount FROM t_user_asset ua WHERE ua.f_userId = 290
- ) ub
- )
- WHERE f_userId = 290
以上问题只针对mysql数据库