Remove Duplicates from Table

最新推荐文章于 2021-03-29 08:44:24 发布

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本文介绍了一种方法，通过SQL查询来删除数据库表中重复的电子邮件记录。以名为Person的表为例，该表包含id和email两个字段，id为主键。文章探讨了如何仅保留每个电子邮件地址的第一条记录，并给出了具体的SQL代码示例。

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Remove Duplicates from Table

[Description]
You are give a table named Person

Code: Select all

[Description]
You are give a table named Person

Code: Select all
+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| email       | varchar |
| id          | int     |
+-------------+---------+

id is the primary key column for this table.

Write a SQL to delete all the duplicated email records

id is the primary key column for this table.

Write a SQL to delete all the duplicated email records

For example, if the rows are:

For example, if the rows are:
+----+-------------+
| 1  | a@gmail.com |
| 2  | b@gmail.com |
| 3  | a@gmail.com |
| 4  | b@gmail.com |
+----+-------------+

Does deleting duplicate email records mean deleting all duplicates except the first entry?
+----+-------------+
| 1  | a@gmail.com |
| 2  | b@gmail.com |
+----+-------------+

Or we don't care if the deleted entry is not the first one, such as this is correct too?
+----+-------------+
| 3  | a@gmail.com |
| 4  | b@gmail.com |
+----+-------------+