mysql查询与2个对象为同一个表

Question

 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.


# Write your MySQL query statement below
DELETE p1
FROM Person p1, Person p2
WHERE p1.Email = p2.Email AND
p1.Id > p2.Id

这是一个SQL问题和解决方案。 我的问题是：为什么我们需要p1和p2两个对象？这个查询在这里使用什么概念？当然它不是表连接子查询。 我不熟悉这种查询模式。希望有人给我一些关于此类查询的指针或链接。感谢