Duplicate Emails

    Write a SQL query to find all duplicate emails in a table named Person.    +----+---------+    | Id | Email   |    +----+---------+    | 1  | [e-mail] |    | 2  | [e-mail] |    | 3  | [e-mail] |    +----+---------+    For example, your query should return the following for the above table:    +---------+    | Email   |    +---------+    | [e-mail] |    +---------+Note: All emails are in lowercase.    主要是group by的应用    select Email from ( select Email,count(Email) as cnt from Person group by Email ) t where cnt>1;    或者    select Email from ( select Email,count(Email) as cnt from Person group by Email having cnt>1) t ;    order by 要在group by 之后使用，不能在group by之前使用。    select Email from ( select Email,count(Email) as cnt from Person order by Email group by Email ) t where cnt>1;    这个执行会有问题。