SQL实现LeetCode(196.删除重复邮箱)

[leetcode] 196.delete duplicate emails 删除重复邮箱

write a sql query to delete all duplicate email entries in a table named person, keeping only unique emails based on its smallest id.

+----+------------------+
| id | email            |
+----+------------------+
| 1  | [e-mail] |
| 2  | [e-mail]  |
| 3  | [e-mail] |
+----+------------------+
id is the primary key column for this table.

for example, after running your query, the above person table should have the following rows:

+----+------------------+
| id | email            |
+----+------------------+
| 1  | [e-mail] |
| 2  | [e-mail]  |
+----+------------------+

这道题让我们删除重复邮箱，那我们可以首先找出所有不重复的邮箱，然后取个反就是重复的邮箱，都删掉即可，那么我们如何找出所有不重复的邮箱呢，我们可以按照邮箱群组起来，然后用min关键字挑出较小的，然后取补集删除即可：

解法一：

delete from person where id not in
(select id from (select min(id) id from person group by email) p);

我们也可以使用内交让两个表以邮箱关联起来，然后把相同邮箱且id大的删除掉，参见代码如下：

解法二：

delete p2 from person p1 join person p2 
on p2.email = p1.email where p2.id > p1.id;

我们也可以不用join，而直接用where将两表关联起来也行：

解法三：

delete p2 from person p1, person p2
where p1.email = p2.email and p2.id > p1.id;

类似题目：

duplicate emails

参考资料：

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