SQL算数运算和逻辑比较

算数运算符和逻辑比较符，可以用于SQL数据的筛查(SELECT) 。 以下用一个例子

来说明 | employee_ID | employee_name | salary | hours | allowance | tax | | — | — | — | — | — | — | | 1 | alex | 24000 | 10 | 1000 | 1000 | | 2 | John | 55000 | 11 | 3000 | 2000 | | 3 | James | 52000 | 7 | 3000 | 2000 | | 4 | Sam | 24000 | 11 | 1000 | 1000 |

SELECT * FROM employee WHERE employee_id = 1; -- 选择员工号为 1 的员工

SELECT * FROM employee WHERE salary * 2 = 48000; -- 选择年薪的两倍48000USD的员工

SELECT * FROM employee WHERE salary + allowance - tax >= 48000; -- 净收入大于于48000

SELECT * FROM employee WHERE employee_name = 'James';  找到'James'的相关信息