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 p1using Person p1 inner join Person p2on p1.Id > p2.Id and p1.Email = p2.Email