SQL27 查看不同年龄段的用户明细

携手创作,共同成长！这是我参与「掘金日新计划 · 8 月更文挑战」的第3天,点击查看活动详情

️‍欢迎订阅java厂长《SQL每日一题》 ️‍

1、题目

现在运营想要将用户划分为20岁以下,20-24岁,25岁及以上三个年龄段,分别查看不同年龄段用户的明细情况,请取出相应数据.

（注：若年龄为空请返回其他.）

示例：user_profile

id	device_id	gender	age	university	gpa	active_days_within_30	question_cnt	answer_cnt
1	2138	male	21	北京大学	3.4	7	2	12
2	3214	male		复旦大学	4	15	5	25
3	6543	female	20	北京大学	3.2	12	3	30
4	2315	female	23	浙江大学	3.6	5	1	2
5	5432	male	25	山东大学	3.8	20	15	70
6	2131	male	28	山东大学	3.3	15	7	13
7	4321	male	26	复旦大学	3.6	9	6	52

根据示例,你的查询应返回以下结果：

device_id	gender	age_cut
2138	male	20-24岁
3214	male	其他
6543	female	20-24岁
2315	female	20-24岁
5432	male	25岁及以上
2131	male	25岁及以上
4321	male	25岁及以上

示例1

输入：
drop table if exists `user_profile`;
drop table if  exists `question_practice_detail`;
CREATE TABLE `user_profile` (
`id` int NOT NULL,
`device_id` int NOT NULL,
`gender` varchar(14) NOT NULL,
`age` int ,
`university` varchar(32) NOT NULL,
`gpa` float,
`active_days_within_30` int ,
`question_cnt` int ,
`answer_cnt` int 
);
CREATE TABLE `question_practice_detail` (
`id` int NOT NULL,
`device_id` int NOT NULL,
`question_id`int NOT NULL,
`result` varchar(32) NOT NULL
);
CREATE TABLE `question_detail` (
`id` int NOT NULL,
`question_id`int NOT NULL,
`difficult_level` varchar(32) NOT NULL
);

INSERT INTO user_profile VALUES(1,2138,'male',21,'北京大学',3.4,7,2,12);
INSERT INTO user_profile VALUES(2,3214,'male',null,'复旦大学',4.0,15,5,25);
INSERT INTO user_profile VALUES(3,6543,'female',20,'北京大学',3.2,12,3,30);
INSERT INTO user_profile VALUES(4,2315,'female',23,'浙江大学',3.6,5,1,2);
INSERT INTO user_profile VALUES(5,5432,'male',25,'山东大学',3.8,20,15,70);
INSERT INTO user_profile VALUES(6,2131,'male',28,'山东大学',3.3,15,7,13);
INSERT INTO user_profile VALUES(7,4321,'male',28,'复旦大学',3.6,9,6,52);
INSERT INTO question_practice_detail VALUES(1,2138,111,'wrong');
INSERT INTO question_practice_detail VALUES(2,3214,112,'wrong');
INSERT INTO question_practice_detail VALUES(3,3214,113,'wrong');
INSERT INTO question_practice_detail VALUES(4,6543,111,'right');
INSERT INTO question_practice_detail VALUES(5,2315,115,'right');
INSERT INTO question_practice_detail VALUES(6,2315,116,'right');
INSERT INTO question_practice_detail VALUES(7,2315,117,'wrong');
INSERT INTO question_practice_detail VALUES(8,5432,117,'wrong');
INSERT INTO question_practice_detail VALUES(9,5432,112,'wrong');
INSERT INTO question_practice_detail VALUES(10,2131,113,'right');
INSERT INTO question_practice_detail VALUES(11,5432,113,'wrong');
INSERT INTO question_practice_detail VALUES(12,2315,115,'right');
INSERT INTO question_practice_detail VALUES(13,2315,116,'right');
INSERT INTO question_practice_detail VALUES(14,2315,117,'wrong');
INSERT INTO question_practice_detail VALUES(15,5432,117,'wrong');
INSERT INTO question_practice_detail VALUES(16,5432,112,'wrong');
INSERT INTO question_practice_detail VALUES(17,2131,113,'right');
INSERT INTO question_practice_detail VALUES(18,5432,113,'wrong');
INSERT INTO question_practice_detail VALUES(19,2315,117,'wrong');
INSERT INTO question_practice_detail VALUES(20,5432,117,'wrong');
INSERT INTO question_practice_detail VALUES(21,5432,112,'wrong');
INSERT INTO question_practice_detail VALUES(22,2131,113,'right');
INSERT INTO question_practice_detail VALUES(23,5432,113,'wrong');
INSERT INTO question_detail VALUES(1,111,'hard');
INSERT INTO question_detail VALUES(2,112,'medium');
INSERT INTO question_detail VALUES(3,113,'easy');
INSERT INTO question_detail VALUES(4,115,'easy');
INSERT INTO question_detail VALUES(5,116,'medium');
INSERT INTO question_detail VALUES(6,117,'easy');

输出：
2138|male|20-24岁
3214|male|其他
6543|female|20-24岁
2315|female|20-24岁
5432|male|25岁及以上
2131|male|25岁及以上
4321|male|25岁及以上
复制代码

2、思路🧠

问题分解：

限定条件：无;
划分年龄段：Numerical condition judgment,Can use multipleif,But it is more convenient to usecase when [expr] then [result1]...else [default] end

解决方法：

IF条件查询

IF(age is null,'其他',
     IF(age<20,'20岁以下',
        IF(age<=24,'20-24岁','25岁及以上')))
复制代码

CASE函数查询,是一种多分支的函数,可以根据条件列表的值返回多个可能的结果表达式中的一个;可用在任何允许使用表达式的地方,但不能单独作为一个语句执行.分为：简单CASE函数、搜索CASE函数

#简单CASE函数
CASE 测试表达式
WHEN 简单表达式1 THEN 结果表达式1
WHEN 简单表达式2 THEN 结果表达式2 ……
WHEN 简单表达式n THEN 结果表达式n
[ ELSE 结果表达式n+1 ]
END

#搜索CASE函数
CASE
WHEN 布尔表达式1 THEN 结果表达式1
WHEN 布尔表达式2 THEN 结果表达式2 ……
WHEN 布尔表达式n THEN 结果表达式n 
[ ELSE 结果表达式n+1 ]
END
复制代码

3、代码

commit AC

SELECT device_id, gender,
	  (case when age <20 then '20岁以下'
       when age >=20 AND age < 25 then '20-24岁'
       when age >=25 then '25岁及以上'
       else '其他' end) AS age_cut
FROM user_profile

SELECT device_id,gender,
  IF(age is null,'其他',
     IF(age<20,'20岁以下',
        IF(age<=24,'20-24岁','25岁及以上'))) age_cut
FROM user_profile
复制代码