SQL-Delete Duplicate Emails

Write a SQL query to delete all duplicate email entries in a table named Person, keeping only unique emails based on its smallest Id.

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
| 3  | john@example.com |
+----+------------------+
Id is the primary key column for this table.

For example, after running your query, the above Person table should have the following rows:

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+

思路：
（1）首先说一下inner join（等价于join），以及他的衍生品left/right join。他们的实质就是在笛卡尔积的基础上加上了附加的条件。
（2）然后就是delete的格式：
delete from table where..

delete 
from p1
using Person p1 inner join Person p2
on p1.Id > p2.Id and p1.Email = p2.Email

SQL-Delete Duplicate Emails

原文：http://www.cnblogs.com/immortal-worm/p/5095255.html