在 MySQL 中添加一个临时列，其值依赖于另一个列?
mysqlmysqli database
您可以使用 CASE 语句来实现此目的，并设置条件以在临时列中获取结果。
首先我们创建一个表 −
mysql> create table DemoTable ( EmployeeId int NOT NULL AUTO_INCREMENT PRIMARY KEY, EmployeeName varchar(20), EmployeeSalary int, EmployeeExperience int ); Query OK, 0 rows affected (0.64 sec)
下面是使用 insert 命令在表中插入一些记录的查询 −
mysql> insert into DemoTable(EmployeeName,EmployeeSalary,EmployeeExperience) values('Larry',4500,5);
Query OK, 1 row affected (0.20 sec)
mysql> insert into DemoTable(EmployeeName,EmployeeSalary,EmployeeExperience) values('Mike',130000,8);
Query OK, 1 row affected (0.21 sec)
mysql> insert into DemoTable(EmployeeName,EmployeeSalary,EmployeeExperience) values('Sam',11000,5);
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable(EmployeeName,EmployeeSalary,EmployeeExperience) values('Carol',140000,8) ;
Query OK, 1 row affected (0.18 sec)
以下是使用 select 命令显示表中记录的查询 −
mysql> select *from DemoTable;
这将产生以下输出 −
+------------+--------------+----------------+--------------------+ | EmployeeId | EmployeeName | EmployeeSalary | EmployeeExperience | +------------+--------------+----------------+--------------------+ | 1 | Larry | 4500 | 5 | | 2 | Mike | 130000 | 8 | | 3 | Sam | 11000 | 5 | | 4 | Carol | 140000 | 8 | +------------+--------------+----------------+--------------------+ 4 rows in set (0.00 sec)
以下是在 MySQL 中添加临时列的查询，其中的值依赖于另一列。这里的临时列是 NewSalary −
mysql> select EmployeeId,EmployeeName,EmployeeSalary,EmployeeExperience, case when EmployeeExperience=5 then EmployeeSalary+10000 when EmployeeExperience=8 then EmployeeSalary+20000 else null end as NewSalary from DemoTable;
这将产生以下输出 −
+------------+--------------+----------------+--------------------+-----------+ | EmployeeId | EmployeeName | EmployeeSalary | EmployeeExperience | NewSalary | +------------+--------------+----------------+--------------------+-----------+ | 1 | Larry | 4500 | 5 | 14500 | | 2 | Mike | 130000 | 8 | 150000 | | 3 | Sam | 11000 | 5 | 21000 | | 4 | Carol | 140000 | 8 | 160000 | +------------+--------------+----------------+--------------------+-----------+ 4 rows in set (0.00 sec)
