不允许在子查询的同时删除原表数据(ERROR 1093 (HY000))

delete from t where userid in (select userid from t where userid < 10);

ERROR 1093 (HY000): You can't specify target table 't' for update in FROM clause

delete from t where userid in (select userid from (select userid from t where userid < 10) tmp );

Query OK, 2 rows affected (0.02 sec)