`

You can't specify target table <tbl> for update in FROM clause

阅读更多
[size=large][/size]

mysql中You can't specify target table <tbl> 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。

原文:
http://blog.csdn.net/priestmoon/article/details/8016121
分享到:
评论

相关推荐

Global site tag (gtag.js) - Google Analytics