如何使用 CASE 语句更新获取的特定列值?
mysqlmysqli database
为此，请使用 UPDATE 命令和 CASE 语句。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 ); Query OK, 0 rows affected (0.00 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable1925(StudentName,StudentMarks) values('Chris',98);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1925(StudentName,StudentMarks) values('David',45);
Query OK, 1 row affected (0.00 sec)
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)
这是使用 CASE 语句获取的更新特定列值的查询 −
mysql> update DemoTable1925 set StudentMarks=case StudentMarks when 45 then 98 when 98 then 0 end where StudentMarks IN(45,98); Query OK, 2 rows affected (0.00 sec) 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)
