如何更新使用CASE语句获取的特定列值？
为此，将UPDATE命令与CASE语句一起使用。让我们首先创建一个表-
mysql> create table DemoTable1925 ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentName varchar(20), StudentMarks int );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable1925(StudentName,StudentMarks) values('Chris',98);
mysql> insert into DemoTable1925(StudentName,StudentMarks) values('David',45);使用select语句显示表中的所有记录-
mysql> select * from DemoTable1925;
这将产生以下输出-
+-----------+-------------+--------------+ | StudentId | StudentName | StudentMarks | +-----------+-------------+--------------+ | 1 | Chris | 98 | | 2 | David | 45 | +-----------+-------------+--------------+ 2 rows in set (0.00 sec)
这是更新使用CASE语句获取的特定列值的查询-
mysql> update DemoTable1925 set StudentMarks=case StudentMarks when 45 then 98 when 98 then 0 end where StudentMarks IN(45,98); Rows matched: 2 Changed: 2 Warnings: 0
让我们再次检查表记录-
mysql> select * from DemoTable1925;
这将产生以下输出-
+-----------+-------------+--------------+ | StudentId | StudentName | StudentMarks | +-----------+-------------+--------------+ | 1 | Chris | 0 | | 2 | David | 98 | +-----------+-------------+--------------+ 2 rows in set (0.00 sec)