196. 删除重复的电子邮箱 | Delete Duplicate Emails

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  | [email protected] |
| 2  | [email protected]  |
| 3  | [email protected] |
+----+------------------+
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  | [email protected] |
| 2  | [email protected]  |
+----+------------------+

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | [email protected] |
| 2  | [email protected]  |
| 3  | [email protected] |
+----+------------------+
Id 是这个表的主键。

例如，在运行你的查询语句之后，上面的 Person 表应返回以下几行:

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

517ms

1 DELETE
2 FROM person
3 WHERE id NOT IN (SELECT t.id
4                  FROM (
5                         SELECT min(id) AS id
6                         FROM Person
7                         GROUP BY email
8                       ) t);

 1 # Write your MySQL query statement below
 2 DELETE
 3 FROM Person
 4 WHERE Id IN (
 5     SELECT Id
 6     FROM (
 7         SELECT
 8         Id, Email, (Email = @prev) AS dup, @prev := Email
 9         FROM (
10             SELECT Email, Id
11             FROM Person
12             ORDER BY 1, 2
13         ) AS sorted,
14         (SELECT @prev := NULL) AS init
15     ) AS t
16     WHERE dup IS TRUE
17 )

1 # Write your MySQL query statement below
2 delete from Person where Id not in(select t.Id from (select min(Id) id from Person b group by Email) t)

原文地址：https://www.cnblogs.com/strengthen/p/9744408.html