leetcode182. 查找重复的电子邮箱（SQL)

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。

思路：自连接，id不同邮箱相同即可找到。

select distinct A.email
from Person as A,Person as B
where A.Id<>B.Id and A.Email=B.Email;

或分组，条件是出现次数大于一：

select Email
from Person
group by Email
having count(Email) > 1;