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法律在 MySQL 中添加一个临时列，而该列的值取决于另一列？
为此，你可以使用 CASE 语句，并设置条件在临时列中获取结果。
首先让我们创建一个表格 -
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)
以下是使用插入命令在表格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)以下是使用选择命令从表格中显示记录的查询 -
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)
以下是添加一个临时列的查询，并且该列的值取决于另一列。此处的临时列是 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)
更新于: 30-7-2019
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