182. 查找重复的电子邮箱(Duplicate Emails)

题目难度： 简单

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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  | a@b.com |
| 2  | c@d.com |
| 3  | a@b.com |
+----+---------+

根据以上输入，你的查询应返回以下结果：

+---------+
| Email   |
+---------+
| a@b.com |
+---------+

**说明：**所有电子邮箱都是小写字母。

Solution

Language: MySQL

# 1st
SELECT Email FROM Person GROUP BY Email
HAVING COUNT(*) > 1;
​
# 2nd
SELECT DISTINCT p1.Email FROM Person p1
JOIN Person p2 ON p1.Email = p2.Email
WHERE p1.Id <> p2.Id;
​