196. Delete Duplicate Emails
表结构
+----+------------------+
| Id | Email |
+----+------------------+
| 1 | john@example.com |
| 2 | bob@example.com |
| 3 | john@example.com |
+----+------------------+
问题描述
删除Person表中重复的邮件，只保留唯一一个邮件。
+----+------------------+
| Id | Email |
+----+------------------+
| 1 | john@example.com |
| 2 | bob@example.com |
+----+------------------+
解决方案
子查询方式：
delete from Person
where Id not in
(select Id from
(select min(Id) as Id
from Person
group by Email
) p
);
表关联方式：
delete p1
from Person p1,Person p2
where p1.Email=p2.Email and p1.Id>p2.Id
总结
之前学习的都是查询操作，本篇主要是删除操作