sql查找重复数据 group by having

leetcode:找到名字重复的邮箱名

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.

方法1:

select Email from
(select Email,count( Email) as count from Person group by Email )as P
where count !=1;

方法2

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