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如何使用LEFT JOIN从MySQL表中删除重复值？

2024-04-20 14:39:04 365

让我们首先创建一个表-

mysql> create table DemoTable
(
   Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   FirstName varchar(100)
);

使用插入命令在表中插入一些记录-

mysql> insert into DemoTable(FirstName) values('Chris');
mysql> insert into DemoTable(FirstName) values('Robert');
mysql> insert into DemoTable(FirstName) values('Robert');
mysql> insert into DemoTable(FirstName) values('John');
mysql> insert into DemoTable(FirstName) values('John');
mysql> insert into DemoTable(FirstName) values('Mike');

使用select语句显示表中的所有记录-

mysql> select *from DemoTable;

这将产生以下输出-

+----+-----------+
| Id | FirstName |
+----+-----------+
|  1 | Chris     |
|  2 | Robert    |
|  3 | Robert    |
|  4 | John      |
|  5 | John      |
|  6 | Mike      |
+----+-----------+
6 rows in set (0.00 sec)

以下是从MySQL表中删除重复值的查询-

mysql> delete tbl from DemoTable tbl
left join(
   select min(Id) as Id, FirstName
   from DemoTable
   group by FirstName
) tbl1 ON tbl.Id = tbl1.Id AND tbl.FirstName = tbl1.FirstName
where tbl1.Id IS NULL;

让我们再次检查表记录。

mysql> select *from DemoTable;

这将产生以下输出-

+----+-----------+
| Id | FirstName |
+----+-----------+
|  1 | Chris     |
|  2 | Robert    |
|  4 | John      |
|  6 | Mike      |
+----+-----------+
4 rows in set (0.00 sec)

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如何使用LEFT JOIN从MySQL表中删除重复值？

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