MySQL常用语句

1.CASE WHEN

-- 1. 简单函数
-- CASE [col_name] WHEN [value1] THEN [result1]…ELSE [default] END
SELECT
	stu_name AS '人物',  -- AS可省略
	(CASE
		stu_name
		WHEN '路明非' THEN
			'S' 
		WHEN '路鸣泽' THEN
			'SSS' 
		WHEN '楚子航' THEN
			'A' 	
		WHEN '凯撒' THEN
			'A' 
		WHEN '芬格尔' THEN
			'A' 
-- 		ELSE '无' 
	END) AS '言灵' 			-- AS可省略
FROM
	edu_student

-- 2. 搜索函数
-- CASE WHEN [expr] THEN [result1]…ELSE [default] END
SELECT 
	stu_name AS '人物',
	stu_age AS '年龄',
	(CASE 
	WHEN stu_age < 18 THEN
		'少年'
	WHEN stu_age < 30 THEN
		'青年'
	WHEN stu_age >= 30 AND stu_age <50 THEN
		'中年'
		ELSE '老年'
	END) AS '状态'
FROM edu_student;