182. Duplicate Emails

原题链接：https://leetcode.com/problems/duplicate-emails/description/
这么简单的题目，我竟然都不会。。。sql 玩的不够溜啊。然后就去看了官方答案吧：
两种方法：

# Write your MySQL query statement below
select Email from 
(select Email, count(Email) as num from Person group by Email) temp where num > 1;

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