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.
分析：分组（Group by） 加 统计（Count）即可
SQL
SELECT Email FROM Person GROUP BY Email Having count(*)>1
[LeetCode] [SQL]: 182: Duplicate Emails
原文：http://www.cnblogs.com/savageclc26/p/4926083.html