LeetCode 182. Duplicate Emails

问题描述：

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.

分析：这是典型的选择重复记录的数据库问题。这个问题还可以拓展一下，如果是获取多个字段同时相同（“与”）的记录，又该如何写呢？在解答中给出多个字段同时相同的记录的方法

解答：

本题解答：

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

选择多个字段同时相同（全部选择）：

select * from tablename a where (a.col1,a.col2) in (select col1,col2 from table group by col1, col2 having count(*) > 1)