#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)