mysql 数据操作 单表查询 通过四则运算查询

#通过四则运算查询

SELECT name, salary*12 FROM employee;
    SELECT name, salary*12 AS Annual_salary FROM employee;
    SELECT name, salary*12 Annual_salary FROM employee;

查看年薪
salary*12

mysql> select name,salary*12 from employee;
+------------+-------------+
| name       | salary*12   |
+------------+-------------+
| alex       | 12000003.72 |
| yuanhao    |    42000.00 |
| liwenzhou  |    25200.00 |
| jingliyang |   108000.00 |
| jinxin     |   360000.00 |
| 成龙       |   120000.00 |
| 歪歪       |    36001.56 |
| 丫丫       |    24004.20 |
| 丁丁       |    12004.44 |
| 星星       |    36003.48 |
| 格格       |    48003.96 |
| 张野       |   120001.56 |
| 程咬金     |   240000.00 |
| 程咬银     |   228000.00 |
| 程咬铜     |   216000.00 |
| 程咬铁     |   204000.00 |
+------------+-------------+
16 rows in set (0.10 sec)

查出来的结果 这是一张虚拟表 

因为查出来结果 标注红色的 salary*12 不太直观 利用另外一种方式查表

 

as 给字段起别名

 

select 字段 as 别名 from 表名

mysql> select name,salary*12 as Annual_salary from employee;
+------------+---------------+
| name       | Annual_salary |
+------------+---------------+
| alex       |   12000003.72 |
| yuanhao    |      42000.00 |
| liwenzhou  |      25200.00 |
| jingliyang |     108000.00 |
| jinxin     |     360000.00 |
| 成龙       |     120000.00 |
| 歪歪       |      36001.56 |
| 丫丫       |      24004.20 |
| 丁丁       |      12004.44 |
| 星星       |      36003.48 |
| 格格       |      48003.96 |
| 张野       |     120001.56 |
| 程咬金     |     240000.00 |
| 程咬银     |     228000.00 |
| 程咬铜     |     216000.00 |
| 程咬铁     |     204000.00 |
+------------+---------------+
16 rows in set (0.10 sec)

不加as也可以 默认后面就是别名

mysql> select name,salary*12 Annual_salary from employee;
+------------+---------------+
| name       | Annual_salary |
+------------+---------------+
| alex       |   12000003.72 |
| yuanhao    |      42000.00 |
| liwenzhou  |      25200.00 |
| jingliyang |     108000.00 |
| jinxin     |     360000.00 |
| 成龙       |     120000.00 |
| 歪歪       |      36001.56 |
| 丫丫       |      24004.20 |
| 丁丁       |      12004.44 |
| 星星       |      36003.48 |
| 格格       |      48003.96 |
| 张野       |     120001.56 |
| 程咬金     |     240000.00 |
| 程咬银     |     228000.00 |
| 程咬铜     |     216000.00 |
| 程咬铁     |     204000.00 |
+------------+---------------+
16 rows in set (0.00 sec)