LeetCode：Delete Duplicate Emails - 删除重复的邮箱数据

时间 2019-11-06

标签 leetcode delete duplicate emails 删除重复邮箱数据繁體版

原文原文链接

一、题目名称sql

Delete Duplicate Emails（删除重复的邮箱数据）数据库

二、题目地址this

https://leetcode.com/problems/delete-duplicate-emails/命令行

三、题目内容code

写一个SQL删除表Person中全部的重复数据，对于重复的数据只保留Id最小的数据ci

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
| 3  | john@example.com |
+----+------------------+
Id is the primary key column for this table.

例如，在执行完该SQL后，表中剩余数据以下：leetcode

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+

四、初始化数据库脚本get

在MySQL数据库中创建一个名为LEETCODE的数据库，用MySQL命令行中的source命令执行下面脚本：table

-- 执行脚本前必须创建名为LEETCODE的DATABASE
USE LEETCODE;
  
DROP TABLE IF EXISTS Person;
CREATE TABLE Person (
  Id INT NOT NULL PRIMARY KEY,
  Email VARCHAR(50)
);

-- INSERT INTO Person (Id, Email) VALUES (1, 'john@example.com');
-- INSERT INTO Person (Id, Email) VALUES (2, 'bob@example.com');
-- INSERT INTO Person (Id, Email) VALUES (3, 'john@example.com');
INSERT INTO Person (Id, Email) VALUES (1, 'tsybius@example.com');
INSERT INTO Person (Id, Email) VALUES (2, 'tsybius@example.com');

五、解题SQL1class

下面是一个比较简单的写法

DELETE P2 FROM Person AS P1, Person AS P2
WHERE  P1.Email = P2.Email AND
       P1.Id < P2.Id;

六、解题SQL2

另外一种写法是使用 NOT IN 来写，但下面的写法是有问题的，放在MySQL中执行时会报错

DELETE FROM Person
WHERE  Id NOT IN (SELECT MIN(ID) MIN_ID
                  FROM   Person
                  GROUP  BY Email)

报错信息以下：

ERROR 1093 (HY000): You can't specify target table 'Person' for update in FROM clause

这是由于SELECT语句不能直接出如今UPDATE语句（DELETE语句也是同样）的WHERE子句中，把SQL改为下面这样就能够AC了：

DELETE FROM Person
WHERE  Id NOT IN (SELECT TMP.MIN_ID
                  FROM   (SELECT MIN(ID) MIN_ID
                          FROM   Person
                          GROUP  BY Email) TMP);

END