mysql删除重复数据保留id最小（最大）的数据

如题：

有Person表

+----+---------+
| Id | Email   |
+----+---------+
| 1  | [email protected] |
| 2  | [email protected] |
| 3  | [email protected] |
+----+---------+

问题：删除重复的邮件地址

这类问题在数据库的笔试题中经常会遇见，解题思路有两个，一连接，二子查询

连接

DELETE p1
FROM
    Person p1,
    Person p2
WHERE
    p1.Email = p2.Email
    AND p1.Id > p2.Id

子查询

DELETE
FROM
    Person
WHERE
    id NOT IN ( SELECT id FROM ( SELECT min( id ) AS id FROM Person GROUP BY email ) AS m );

应该注意的是上述解法额外嵌套了一个 SELECT 语句，如果不这么做，会出现错误：You can't specify target table 'Person' for update in FROM clause。以下演示了这种错误解法。

DELETE
FROM
    Person
WHERE
    id NOT IN ( SELECT min( id ) AS id FROM Person GROUP BY email );

因为mysql中，不能先select一个表的记录，在按此条件进行更新和删除同一个表的记录。解决办法是，将select得到的结果，再通过中间表select一遍，这样就规避了错误，这个问题只出现于mysql，mssql和oracle不会出现此问题。