2019.12.11 LeetCode 从零单刷个人笔记整理(持续更新)
github:https://github.com/ChopinXBP/LeetCode-Babel
编写一个 SQL 查询,来删除 Person 表中所有重复的电子邮箱,重复的邮箱里只保留 Id 最小 的那个。
+----+------------------+
| 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] |
+----+------------------+
DELETE p1
FROM Person p1, Person p2
WHERE p1.email = p2.email AND p1.Id > p2.Id;
#MySQL不允许select和delete操作同一个表,会出现以下错误
#错误:You can't specify target table 'person' for update in FROM clause
#解决办法:添加一个临时表
DELETE FROM Person
WHERE Id NOT IN(
SELECT Id
FROM(
SELECT MIN(Id) AS id
FROM Person
GROUP BY Email
) temp
);
#Coding一小时,Copying一秒钟。留个言点个赞呗,谢谢你#