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

使用mysql在删除表中重复记录

delete from user where username in (select user name form(select username from user group by username having count(username)>1));

遇到mysql报错You can't specify target table for update in FROM clause

上网百度了下原来是mysql中不允许先select出同一表中的某些值，再update这个表(在同一语句中)，这个问题只出现于mysql，sqlserver和oracle不会出现此问题

解决办法：将select出的结果再通过中间表select一遍

delete from user where username in (select a.username from(select username from user group by username having count(username)>1)a);

这样delete和select的就不是同一个表了