mysql中You can’t specify target table for update in FROM clause错误解决方法

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：

1 delete from tbl where id in 
2 (
3         select max(id) from tbl a where EXISTS
4         (
5             select 1 from tbl b where a.tac=b.tac group by tac HAVING count(1)>1
6         )
7         group by tac
8 )

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。

引用自：![脚本之家](http://www.jb51.net/article/60926.htm)