SQL执行报错实例及原因解析

• mysql执行sql:

update t1 set a=(select b-c from t1);

报错：“ERROR 1093 (HY000) at line 15:You can’t specify target table ‘t1’ for update in from clause”
报错原因:对于同一个表的select和update不能出现在同一语句中
修改sql:

update t1 set a=(select b-c from (select b,c from t1 ) tmp);