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  | john@example.com |
| 2  | bob@example.com  |
| 3  | john@example.com |
+----+------------------+
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  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+

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);