Delete Duplicate Emails:SQL删除重复邮件地址

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：
delete p1 from Person p1,Person p2
where p1.Email = p2.Email and p1.Id > p2.Id