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.
用exists
1 select distinct Email from Person p1 where exists (select Id from Person p2 where p1.Email = p2.Email and p1.Id != p2.Id);
用group by
1 select Email from Person group by Email having count(Email) > 1;
原文：http://www.cnblogs.com/luckygxf/p/4324500.html