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：
代码如下: 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：
代码如下: 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 )
