如何使用LEFT JOIN从MySQL表中删除重复值？
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)