mysql数据库中的一些知识点

与Java中的switch...case类比

SELECT salary,department_id, CASE department_id WHEN 30 THEN salary*1.1

WHEN 40 THEN salary*1.2

WHEN 50 THEN salary*1.3

ELSE salary

END "now"

FROM employees ORDER BY department_id

与Java中if...else...if...else..类比

SELECT salary ,

CASE

WHEN salary>20000 THEN ‘A‘

WHEN salary>15000 THEN ‘B‘

WHEN salary>10000 THEN ‘C‘

ELSE ‘D‘

END "de"

FROM employees

mysql中处理时间的函数

SELECT * FROM employees WHERE STR_TO_DATE(‘1992-4-3‘,‘%Y-%c-%d‘)=hiredate;

SELECT * FROM employees WHERE DATE_FORMAT(hiredate,‘%Y-%m-%d‘) =‘1992-04-03‘;

#求两个日期之间的相差天数

DATEDIFF参数为两个日期型

SELECT DATEDIFF(MAX(hiredate),MIN(hiredate)) FROM employees;

原文：https://www.cnblogs.com/liuchaobaidu/p/13491133.html