mysql 1093错误delete from grade where id not in(select id from grade group by userid,degree,subject
mysql 1093错误
delete from grade where id not in(select id from grade group by userid,degree,subject);
出现错误：
ERROR 1093 (HY000): You can't specify target table 'grade' for update in FROM clause
解决办法：
delete from grade where id not in(select id from (select * from grade) ggroup by userid,degree,subject);