一.流程函数

-- 创建表来介绍CREATE TABLE salary (userid INT,salary DECIMAL(9,2));INSERT INTO salary VALUES(1,1000),(2,2000), (3,3000),(4,4000),(5,5000), (1,NULL);SELECT * FROM salary

1. if(value,t,f)  超过2000的用high,否则用low

SELECT IF(salary>2000 ,‘high‘,‘low‘) FROM salary

2. ifnull(value1,value2) 下面语句是把null值替换0

SELECT IFNULL(salary,0) FROM salary;

3.case when ...   用来实现中高低薪的问题

SELECT CASE WHEN salary<=2000 THEN ‘low‘ WHEN salary>=2001 AND salary<=4000 THEN‘middle‘ ELSE ‘high‘ END FROM salary;

二. 其它常用函数

SELECT DATABASE() AS ‘数据库名‘,VERSION() AS ‘数据库版本‘,USER() AS ‘当前用户名‘,INET_ATON(‘192.168.1.1‘)AS ‘IP字节‘,INET_NTOA(3232235777) AS ‘ip字节转IP‘

2. PASSWORD 返回加密后的字符，一般用来设置系统用户的密码

SELECT PASSWORD(‘123456‘)

3. md5(str) 对一般应用数据加密

SELECT MD5(‘123456‘);