leetcode196-Delete Duplicate Emails(删除重复并且id较大的数据)

问题描述：

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  |
+----+------------------+

问题求解：

1、MySQL DELETE语法的多表语法：创造临时表，找到删除条件，进行删除更新。

delete p1 from Person p1 inner join Person p2
where p1.email=p2.email and p1.id>p2.id;

或者：

delete from p1 using Person p1 inner join Person p2
where p1.email=p2.email and p1.id>p2.id;

2、

delete from Person where Id 
not in (select * from (select min(Id) from Person p group by email) mindata);

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