【Leetcode】Duplicate Emails

题目链接：https://leetcode.com/problems/duplicate-emails/

题目：
Write a SQL query to find all duplicate emails in a table named Person.

+—-+———+
| Id | Email |
+—-+———+

| 1 | a@b.com |
| 2 | c@d.com |
| 3 | a@b.com |
+—-+———+
For example, your query should return the following for the above table:

+———+
| Email |
+———+
| a@b.com |
+———+
Note: All emails are in lowercase.

思路：
group by 将数据划分成一组一组的。。那么根据什么来划分呢，就是根据having后面的条件，一般是函数 如count sum

算法：

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