[LeetCode][SQL]Delete Duplicate Emails

Delete Duplicate Emails

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

https://leetcode.com/problems/delete-duplicate-emails/

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##need to link table 'A.Email = B.Email' first !!!!

delete A from Person A, Person B where A.Email = B.Email and A.Id > B.Id

 

delete语句里不能再select这个表，这种写法是过不了的。

delete A from Person A where A.Email in (select B.Email from Person B group by B.Email having count(*) > 1)