select min(id) as id from a group by title;
和
select id from a group by id
执行的结果是一样的,但是下面两条语句的结果就不一样呢?
mysql> delete a,b from (a left join b on a.id=b.aid)
-> left join (select min(id) as id from a group by title) c on a.id=c.id
-> where c.id is null;]
Query OK, 10 rows affected (0.00 sec)
mysql> delete a,b from (a left join b on a.id=b.aid)
-> left join (select id from a group by id) c on a.id=c.id
-> where c.id is null;
Query OK, 0 rows affected (0.00 sec)
这个是我在看帖子的时候看到的 呵呵
http://topic.csdn.net/u/20101008/20/e285fe37-437e-4eab-ab21-98bf1bc70ea2.html?56531
原来是ACMAIN_CHM回答的。。希望能再帮我解答一下 谢谢。。我是新手
-> left join (select id from a group by id) c on a.id=c.id
-> where c.id is null;
Query OK, 0 rows affected (0.00 sec)也是一样的 也是一条都么有删。。
如果把where c.id is null去掉,则全都删除了