目录
leetCode的题目难度不同,为了鼓励自己坚持,所以简单的题目也会放在这里。让老鸟见笑了。
题目
编写一个 SQL 查询,查找 Person 表中所有重复的电子邮箱。
示例:
+----+---------+
| Id | Email |
+----+---------+
| 1 | [email protected] |
| 2 | [email protected] |
| 3 | [email protected] |
+----+---------+
根据以上输入,你的查询应返回以下结果:
+---------+
| Email |
+---------+
| [email protected] |
+---------+
说明:所有电子邮箱都是小写字母。
解
mysql语法
--group by
select Email from Person
group by Email
having count(Email)>1
--自连接
select distinct a.Email
from Person a Person b
where a.Email=b.Email and a.Id <> b.id;