一.流程函數

-- 創建表來介紹
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) 超過2000的用high,否則用low

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

2. ifnull(value1,value2) 下面語句是把null值替換0

SELECT IFNULL(salary,0
 
) FROM salary;

3.case when ... 用來實現中高低薪的問題

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

二. 其它常用函數

SELECT 
DATABASE() AS ‘數據庫名‘,
VERSION() AS ‘數據庫版本‘,
USER() AS ‘當前用戶名‘,
INET_ATON(‘192.168.1.1‘)AS ‘IP字節‘,
INET_NTOA(
 
3232235777) AS ‘ip字節轉IP‘

2. PASSWORD 返回加密後的字符，一般用來設置系統用戶的密碼

SELECT PASSWORD(‘123456‘)

3. md5(str) 對一般應用數據加密

SELECT MD5(‘123456‘);

mysql 開發基礎系列7 流程函數與其它函數