LeetCode: 196. Delete Duplicate Emails

题目描述

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

Note:

Your output is the whole Person table after executing your sql. Use delete statement.

解题思路

-- 删除部分数据行的搜索型 DELETE
-- DELETE语句的删除对象并不是表或者列，而是记录（行）
DELETE FROM <表名> WHERE <条件>;

AC 代码

DELETE P2 FROM Person AS P1, Person AS P2 WHERE P1.Id < P2.Id AND P1.Email = P2.Email;