MySQL：使用分组依据更新字段？

要使用GROUP BY更新字段，请在UPDATE命令中使用ORDER BY LIMIT-

mysql> create table DemoTable2018
   -> (
   -> EmployeeId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> EmployeeName varchar(20),
   -> EmployeeSalary int
   -> );

使用插入命令在表中插入一些记录-

mysql> insert into DemoTable2018(EmployeeName,EmployeeSalary) values('Chris',10000);

mysql> insert into DemoTable2018(EmployeeName,EmployeeSalary) values('David',12560);

mysql> insert into DemoTable2018(EmployeeName,EmployeeSalary) values('Chris',25400);

使用select语句显示表中的所有记录-

mysql> select *from DemoTable2018;

这将产生以下输出-

+------------+--------------+----------------+
| EmployeeId | EmployeeName | EmployeeSalary |
+------------+--------------+----------------+
| 1          | Chris       | 10000           |
| 2          | David       | 12560           |
| 3          | Chris       | 25400           |
+------------+--------------+----------------+
3 rows in set (0.00 sec)

这是对MySQL更新字段的查询-

mysql> update DemoTable2018
   -> set EmployeeSalary=EmployeeSalary+2500 where EmployeeName='Chris'
   -> order by EmployeeId limit 1;
Rows matched: 1 Changed: 1 Warnings: 0

让我们再次检查表记录-

mysql> select *from DemoTable2018;

这将产生以下输出-

+------------+--------------+----------------+
| EmployeeId | EmployeeName | EmployeeSalary |
+------------+--------------+----------------+
| 1          | Chris        | 12500          |
| 2          | David        | 12560          |
| 3          | Mike         | 25400          |
+------------+--------------+----------------+
3 rows in set (0.00 sec)