You can't specify target table 'A' for update in FROM clause

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。