当前位置：网站首页>Tutorial on the principle and application of database system (062) -- MySQL exercise questions: operation questions 32-38 (6)
Tutorial on the principle and application of database system (062) -- MySQL exercise questions: operation questions 32-38 (6)
2022-07-28 13:45:00 【Rsda DBA_ WGX】
Database system principle and Application Tutorial （062）—— MySQL Exercises ： Operation questions 32-38（ 6、 ... and ）
32、 Subquery
subject ： Query the minimum of each school gpa, Output results by university Ascending order .
Example ：user_profile The data in the table are as follows .
| id | device_id | gender | age | university | gpa | active_days_within_30 | question_cnt | answer_cnt |
|---|---|---|---|---|---|---|---|---|
| 1 | 2138 | male | 21 | Peking University, | 3.4 | 7 | 2 | 12 |
| 2 | 3214 | male | Fudan University | 4 | 15 | 5 | 25 | |
| 3 | 6543 | female | 20 | Peking University, | 3.2 | 12 | 3 | 30 |
| 4 | 2315 | female | 23 | Zhejiang University | 3.6 | 5 | 1 | 2 |
| 5 | 5432 | male | 25 | Shandong University | 3.8 | 20 | 15 | 70 |
| 6 | 2131 | male | 28 | Shandong University | 3.3 | 15 | 7 | 13 |
| 7 | 4321 | female | 26 | Fudan University | 3.6 | 9 | 6 | 52 |
The query should return the following results ：
| device_id | university | gpa |
|---|---|---|
| 6543 | Peking University, | 3.2000 |
| 4321 | Fudan University | 3.6000 |
| 2131 | Shandong University | 3.3000 |
| 2315 | Zhejiang University | 3.6000 |
Table structure and data are as follows ：
/* drop table if exists user_profile; 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 ); INSERT INTO user_profile VALUES(1,2138,'male',21,' Peking University, ',3.4,7,2,12); INSERT INTO user_profile VALUES(2,3214,'male',null,' Fudan University ',4.0,15,5,25); INSERT INTO user_profile VALUES(3,6543,'female',20,' Peking University, ',3.2,12,3,30); INSERT INTO user_profile VALUES(4,2315,'female',23,' Zhejiang University ',3.6,5,1,2); INSERT INTO user_profile VALUES(5,5432,'male',25,' Shandong University ',3.8,20,15,70); INSERT INTO user_profile VALUES(6,2131,'male',28,' Shandong University ',3.3,15,7,13); INSERT INTO user_profile VALUES(7,4321,'male',28,' Fudan University ',3.6,9,6,52); */
answer ：
/* select a.device_id, b.university, round(b.gpa,4) gpa from user_profile a join (select university, min(gpa) gpa from user_profile group by university) b on a.gpa = b.gpa and a.university = b.university order by a.university; */
mysql> select a.device_id, b.university, round(b.gpa,4) gpa
-> from user_profile a join
-> (select university, min(gpa) gpa
-> from user_profile group by university) b
-> on a.gpa = b.gpa and a.university = b.university
-> order by a.university;
+-----------+--------------+--------+
| device_id | university | gpa |
+-----------+--------------+--------+
| 6543 | Peking University, | 3.2000 |
| 4321 | Fudan University | 3.6000 |
| 2131 | Shandong University | 3.3000 |
| 2315 | Zhejiang University | 3.6000 |
+-----------+--------------+--------+
4 rows in set (0.00 sec)
33、 Group query and statistics （1）
subject ： Query every user of Fudan University in 8 The number of questions practiced in the month and the number of questions answered correctly , Take out the corresponding detailed data . For in 8 Users who haven't practiced in this month , Answer number result return 0.
Example ：user_profile The data in the table are as follows .
| id | device_id | gender | age | university | gpa | active_days_within_30 |
|---|---|---|---|---|---|---|
| 1 | 2138 | male | 21 | Peking University, | 3.4 | 7 |
| 2 | 3214 | male | Fudan University | 4.0 | 15 | |
| 3 | 6543 | female | 20 | Peking University, | 3.2 | 12 |
| 4 | 2315 | female | 23 | Zhejiang University | 3.6 | 5 |
| 5 | 5432 | male | 25 | Shandong University | 3.8 | 20 |
| 6 | 2131 | male | 28 | Shandong University | 3.3 | 15 |
| 7 | 4321 | female | 26 | Fudan University | 3.6 | 9 |
Example ：question_practice_detail The data in the table are as follows .
| id | device_id | question_id | result | date |
|---|---|---|---|---|
| 1 | 2138 | 111 | wrong | 2021-05-03 |
| 2 | 3214 | 112 | wrong | 2021-05-09 |
| 3 | 3214 | 113 | wrong | 2021-06-15 |
| 4 | 6543 | 111 | right | 2021-08-13 |
| 5 | 2315 | 115 | right | 2021-08-13 |
| 6 | 2315 | 116 | right | 2021-08-14 |
| 7 | 2315 | 117 | wrong | 2021-08-15 |
| …… |
The query should return the following results ：
| device_id | university | question_cnt | right_question_cnt |
|---|---|---|---|
| 3214 | Fudan University | 3 | 0 |
| 4321 | Fudan University | 0 | 0 |
Table structure and data are as follows ：
/* 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 ); CREATE TABLE `question_practice_detail` ( `id` int NOT NULL, `device_id` int NOT NULL, `question_id`int NOT NULL, `result` varchar(32) NOT NULL, `date` date NOT NULL ); INSERT INTO user_profile VALUES(1,2138,'male',21,' Peking University, ',3.4,7); INSERT INTO user_profile VALUES(2,3214,'male',null,' Fudan University ',4.0,15); INSERT INTO user_profile VALUES(3,6543,'female',20,' Peking University, ',3.2,12); INSERT INTO user_profile VALUES(4,2315,'female',23,' Zhejiang University ',3.6,5); INSERT INTO user_profile VALUES(5,5432,'male',25,' Shandong University ',3.8,20); INSERT INTO user_profile VALUES(6,2131,'male',28,' Shandong University ',3.3,15); INSERT INTO user_profile VALUES(7,4321,'male',28,' Fudan University ',3.6,9); INSERT INTO question_practice_detail VALUES(1,2138,111,'wrong','2021-05-03'); INSERT INTO question_practice_detail VALUES(2,3214,112,'wrong','2021-05-09'); INSERT INTO question_practice_detail VALUES(3,3214,113,'wrong','2021-06-15'); INSERT INTO question_practice_detail VALUES(4,6543,111,'right','2021-08-13'); INSERT INTO question_practice_detail VALUES(5,2315,115,'right','2021-08-13'); INSERT INTO question_practice_detail VALUES(6,2315,116,'right','2021-08-14'); INSERT INTO question_practice_detail VALUES(7,2315,117,'wrong','2021-08-15'); INSERT INTO question_practice_detail VALUES(8,3214,112,'wrong','2021-05-09'); INSERT INTO question_practice_detail VALUES(9,3214,113,'wrong','2021-08-15'); INSERT INTO question_practice_detail VALUES(10,6543,111,'right','2021-08-13'); INSERT INTO question_practice_detail VALUES(11,2315,115,'right','2021-08-13'); INSERT INTO question_practice_detail VALUES(12,2315,116,'right','2021-08-14'); INSERT INTO question_practice_detail VALUES(13,2315,117,'wrong','2021-08-15'); INSERT INTO question_practice_detail VALUES(14,3214,112,'wrong','2021-08-16'); INSERT INTO question_practice_detail VALUES(15,3214,113,'wrong','2021-08-18'); INSERT INTO question_practice_detail VALUES(16,6543,111,'right','2021-08-13'); */
answer ：
/* select u.device_id, u.university, count(question_id) question_cnt, sum(if(q.result = 'right', 1, 0)) right_question_cnt from user_profile u left join question_practice_detail q on u.device_id = q.device_id where u.university = ' Fudan University ' and (month(q.date) = 8 or month(q.date) is null) group by u.device_id, u.university; */
mysql> select u.device_id, u.university,
-> count(question_id) question_cnt,
-> sum(if(q.result = 'right', 1, 0)) right_question_cnt
-> from user_profile u left join question_practice_detail q
-> on u.device_id = q.device_id
-> where u.university = ' Fudan University ' and (month(q.date) = 8 or month(q.date) is null)
-> group by u.device_id, u.university;
+-----------+--------------+--------------+--------------------+
| device_id | university | question_cnt | right_question_cnt |
+-----------+--------------+--------------+--------------------+
| 3214 | Fudan University | 3 | 0 |
| 4321 | Fudan University | 0 | 0 |
+-----------+--------------+--------------+--------------------+
2 rows in set (0.00 sec)
/*
explain ：
（1）count(question_id)： Not available here count(*), because count(*) Statistics are all records , And of course question_id Empty record ,count(question_id) Only statistics question_id Not empty record
（2）where Conditions must be specified ：month(q.date) is null, Otherwise, even if you use left join, Records that do not meet the connection conditions will also be filtered
34、 Group query and statistics （2）
subject ： Query the accuracy of users of Zhejiang University in answering different difficult questions , Take out the corresponding data and output it in ascending order of accuracy .
Example ： user_profile The data in the table are as follows .
| id | device_id | gender | age | university | gpa | active_days_within_30 | question_cnt | answer_cnt |
|---|---|---|---|---|---|---|---|---|
| 1 | 2138 | male | 21 | Peking University, | 3.4 | 7 | 2 | 12 |
| 2 | 3214 | male | Fudan University | 4 | 15 | 5 | 25 | |
| 3 | 6543 | female | 20 | Peking University, | 3.2 | 12 | 3 | 30 |
| 4 | 2315 | female | 23 | Zhejiang University | 3.6 | 5 | 1 | 2 |
| 5 | 5432 | male | 25 | Shandong University | 3.8 | 20 | 15 | 70 |
| 6 | 2131 | male | 28 | Shandong University | 3.3 | 15 | 7 | 13 |
| 7 | 4321 | female | 26 | Fudan University | 3.6 | 9 | 6 | 52 |
Example ： question_practice_detail The data in the table are as follows .
| id | device_id | question_id | result |
|---|---|---|---|
| 1 | 2138 | 111 | wrong |
| 2 | 3214 | 112 | wrong |
| 3 | 3214 | 113 | wrong |
| 4 | 6543 | 111 | right |
| 5 | 2315 | 115 | right |
| 6 | 2315 | 116 | right |
| 7 | 2315 | 117 | wrong |
Example ： question_detail The data in the table are as follows .
| question_id | difficult_level |
|---|---|
| 111 | hard |
| 112 | medium |
| 113 | easy |
| 115 | easy |
| 116 | medium |
| 117 | easy |
The query should return the following results ：
| difficult_level | correct_rate |
|---|---|
| easy | 0.5000 |
| medium | 1.0000 |
Table structure and data are as follows ：
/* drop table if exists `user_profile`; drop table if exists `question_practice_detail`; drop table if exists `question_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, `date` date 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,' Peking University, ',3.4,7,2,12); INSERT INTO user_profile VALUES(2,3214,'male',null,' Fudan University ',4.0,15,5,25); INSERT INTO user_profile VALUES(3,6543,'female',20,' Peking University, ',3.2,12,3,30); INSERT INTO user_profile VALUES(4,2315,'female',23,' Zhejiang University ',3.6,5,1,2); INSERT INTO user_profile VALUES(5,5432,'male',25,' Shandong University ',3.8,20,15,70); INSERT INTO user_profile VALUES(6,2131,'male',28,' Shandong University ',3.3,15,7,13); INSERT INTO user_profile VALUES(7,4321,'male',28,' Fudan University ',3.6,9,6,52); INSERT INTO question_practice_detail VALUES(1,2138,111,'wrong','2021-05-03'); INSERT INTO question_practice_detail VALUES(2,3214,112,'wrong','2021-05-09'); INSERT INTO question_practice_detail VALUES(3,3214,113,'wrong','2021-06-15'); INSERT INTO question_practice_detail VALUES(4,6543,111,'right','2021-08-13'); INSERT INTO question_practice_detail VALUES(5,2315,115,'right','2021-08-13'); INSERT INTO question_practice_detail VALUES(6,2315,116,'right','2021-08-14'); INSERT INTO question_practice_detail VALUES(7,2315,117,'wrong','2021-08-15'); INSERT INTO question_practice_detail VALUES(8,3214,112,'wrong','2021-05-09'); INSERT INTO question_practice_detail VALUES(9,3214,113,'wrong','2021-08-15'); INSERT INTO question_practice_detail VALUES(10,6543,111,'right','2021-08-13'); INSERT INTO question_practice_detail VALUES(11,2315,115,'right','2021-08-13'); INSERT INTO question_practice_detail VALUES(12,2315,116,'right','2021-08-14'); INSERT INTO question_practice_detail VALUES(13,2315,117,'wrong','2021-08-15'); INSERT INTO question_practice_detail VALUES(14,3214,112,'wrong','2021-08-16'); INSERT INTO question_practice_detail VALUES(15,3214,113,'wrong','2021-08-18'); INSERT INTO question_practice_detail VALUES(16,6543,111,'right','2021-08-13'); 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'); */
answer ：
/* select b.difficult_level, round(sum(if(result = 'right', 1, 0))/count(*), 4) correct_rate from question_practice_detail a join question_detail b on a.question_id = b.question_id where a.device_id in (select device_id from user_profile where university = ' Zhejiang University ') group by b.difficult_level order by correct_rate; */
mysql> select b.difficult_level,
-> round(sum(if(result = 'right', 1, 0))/count(*), 4) correct_rate
-> from question_practice_detail a join question_detail b
-> on a.question_id = b.question_id
-> where a.device_id in (select device_id from user_profile where university = ' Zhejiang University ')
-> group by b.difficult_level
-> order by correct_rate;
+-----------------+--------------+
| difficult_level | correct_rate |
+-----------------+--------------+
| easy | 0.5000 |
| medium | 1.0000 |
+-----------------+--------------+
2 rows in set (0.00 sec)
35、 Sort query results （1）
subject ： Query the user age in the user information table , Take out the corresponding data and sort them in ascending order of age .
Example ：user_profile The data in the table are as follows .
| id | device_id | gender | age | university | gpa |
|---|---|---|---|---|---|
| 1 | 2138 | male | 21 | Peking University, | 3.4 |
| 2 | 3214 | male | 23 | Fudan University | 4 |
| 3 | 6543 | female | 20 | Peking University, | 3.2 |
| 4 | 2315 | female | 23 | Zhejiang University | 3.6 |
| 5 | 5432 | male | 25 | Shandong University | 3.8 |
| 6 | 2131 | male | 28 | Beijing Normal University | 3.3 |
The query should return the following results ：
| device_id | age |
|---|---|
| 6534 | 20 |
| 2138 | 21 |
| 3214 | 23 |
| 2315 | 23 |
| 5432 | 25 |
| 2131 | 28 |
Table structure and data are as follows ：
/* drop table if exists user_profile; 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); INSERT INTO user_profile VALUES(1,2138,'male',21,' Peking University, ',3.4); INSERT INTO user_profile VALUES(2,3214,'male',23,' Fudan University ',4.0); INSERT INTO user_profile VALUES(3,6543,'female',20,' Peking University, ',3.2); INSERT INTO user_profile VALUES(4,2315,'female',23,' Zhejiang University ',3.6); INSERT INTO user_profile VALUES(5,5432,'male',25,' Shandong University ',3.8); INSERT INTO user_profile VALUES(6,2131,'male',28,' Beijing Normal University ',3.3); */
answer ：
mysql> select device_id, age from user_profile order by age;
+-----------+------+
| device_id | age |
+-----------+------+
| 6543 | 20 |
| 2138 | 21 |
| 3214 | 23 |
| 2315 | 23 |
| 5432 | 25 |
| 2131 | 28 |
+-----------+------+
6 rows in set (0.00 sec)
36、 Sort query results （1）
subject ： Query the age and... In the user information table gpa data , And first according to gpa Ascending sort , Then sort the output in ascending order of age .
Example ：user_profile The data in the table are as follows .
| id | device_id | gender | age | university | gpa |
|---|---|---|---|---|---|
| 1 | 2138 | male | 21 | Peking University, | 3.4 |
| 2 | 3214 | male | 23 | Fudan University | 4 |
| 3 | 6543 | female | 20 | Peking University, | 3.2 |
| 4 | 2315 | female | 23 | Zhejiang University | 3.6 |
| 5 | 5432 | male | 25 | Shandong University | 3.8 |
| 6 | 2131 | male | 28 | Beijing Normal University | 3.3 |
The query should return the following results ：
| device_id | gpa | age |
|---|---|---|
| 6543 | 3.2 | 20 |
| 2131 | 3.3 | 28 |
| 2138 | 3.4 | 21 |
| 2315 | 3.6 | 23 |
| 5432 | 3.8 | 25 |
| 3214 | 4 | 23 |
answer ：
mysql> select device_id, gpa, age from user_profile order by gpa, age;
+-----------+------+------+
| device_id | gpa | age |
+-----------+------+------+
| 6543 | 3.2 | 20 |
| 2131 | 3.3 | 28 |
| 2138 | 3.4 | 21 |
| 2315 | 3.6 | 23 |
| 5432 | 3.8 | 25 |
| 3214 | 4 | 23 |
+-----------+------+------+
6 rows in set (0.00 sec)
37、 Sort query results （3）
subject ： Query the corresponding data in the user information table , And first according to gpa Descending 、 Sort the output in descending order of age .
Example ：user_profile The data in the table are as follows .
| id | device_id | gender | age | university | gpa |
|---|---|---|---|---|---|
| 1 | 2138 | male | 21 | Peking University, | 3.4 |
| 2 | 3214 | male | 23 | Fudan University | 4 |
| 3 | 6543 | female | 20 | Peking University, | 3.2 |
| 4 | 2315 | female | 23 | Zhejiang University | 3.6 |
| 5 | 5432 | male | 25 | Shandong University | 3.8 |
| 6 | 2131 | male | 28 | Beijing Normal University | 3.3 |
The query should return the following results ：
| device_id | gpa | age |
|---|---|---|
| 3214 | 4 | 23 |
| 5432 | 3.8 | 25 |
| 2315 | 3.6 | 23 |
| 2138 | 3.4 | 21 |
| 2131 | 3.3 | 28 |
| 6543 | 3.2 | 20 |
answer ：
mysql> select device_id, gpa, age from user_profile order by gpa desc, age desc;
+-----------+------+------+
| device_id | gpa | age |
+-----------+------+------+
| 3214 | 4 | 23 |
| 5432 | 3.8 | 25 |
| 2315 | 3.6 | 23 |
| 2138 | 3.4 | 21 |
| 2131 | 3.3 | 28 |
| 6543 | 3.2 | 20 |
+-----------+------+------+
6 rows in set (0.00 sec)
38、 The use of aggregate functions
subject ： Inquire about 2021 year 8 The total number of users who have practiced the topic and the total number of times they have practiced the topic in the month , Take out the corresponding results .
Example ：question_practice_detail The data in the table are as follows .
| id | device_id | question_id | result | date |
|---|---|---|---|---|
| 1 | 2138 | 111 | wrong | 2021-05-03 |
| 2 | 3214 | 112 | wrong | 2021-05-09 |
| 3 | 3214 | 113 | wrong | 2021-06-15 |
| 4 | 6543 | 111 | right | 2021-08-13 |
| 5 | 2315 | 115 | right | 2021-08-13 |
| 6 | 2315 | 116 | right | 2021-08-14 |
| 7 | 2315 | 117 | wrong | 2021-08-15 |
| …… |
The query should return the following results ：
| did_cnt | question_cnt |
|---|---|
| 3 | 12 |
answer ：
/* select count(distinct device_id) did_cnt, count(*) question_cnt from question_practice_detail where date between '2021-8-1' and '2021-8-31'; */
mysql> select count(distinct device_id) did_cnt,
-> count(*) question_cnt
-> from question_practice_detail
-> where date between '2021-8-1' and '2021-8-31';
+---------+--------------+
| did_cnt | question_cnt |
+---------+--------------+
| 3 | 12 |
+---------+--------------+
1 row in set (0.02 sec)
边栏推荐
- Leetcode · daily question · 1331. array sequence number conversion · discretization
- 数据库系统原理与应用教程（059）—— MySQL 练习题：操作题 1-10（三）
- 少儿编程 电子学会图形化编程等级考试Scratch二级真题解析（判断题）2022年6月
- Map tiles: detailed explanation of vector tiles and grid tiles
- 使用 Fail2ban 保护 Web 服务器免受 DDoS 攻击
- C language: merge sort
- JWT login authentication + token automatic renewal scheme, well written!
- Debezium系列之：2.0.0.Beta1的重大变化和新特性
- Beyond istio OSS -- current situation and future of istio Service Grid
- I miss the year of "losing" Li Ziqi
猜你喜欢
酷炫操作预热！代码实现小星球特效
屈辱、抗争、逆转，三十年，中国该赢微软一次了
30天刷题计划（三）
Half wave rectification light LED
Countdown 2 days! 2022 China Computing Conference: Mobile cloud invites you to meet with computing network for innovative development
Beyond Istio OSS——Istio服务网格的现状与未来
严格模式——let和const——箭头函数——解构赋值——字符串模板symbol——Set和Map——生成器函数
【黑马早报】字节估值缩水，降至2700亿美元；“二舅”视频作者回应抄袭；任泽平称取消商品房预售制是大势所趋；美联储宣布再加息75个基点...
jar包
SQL每日一练（牛客新题库）——第4天：高级操作符
随机推荐
C语言：随机生成数+归并排序
SQL daily practice (Niuke new question bank) - day 4: advanced operators
30天刷题计划（二）
Today's sleep quality record 75 points
记一次使用pdfbox解析pdf,获取pdf的关键数据的工具使用
Jenkins--持续集成服务器
功率放大器和匹配网络学习
Dry goods -- encapsulated anti shake and throttling method in the project
蓝桥集训（附加面试题）第七天
无法连接服务器怎么办(原始服务器找不到目标资源)
Some thoughts on.Net desktop development
111. The sap ui5 fileuploader control realizes local file upload and encounters a cross domain access error when receiving the response from the server
DOJP1520星门跳跃题解
30天刷题训练（一）
POJ3268最短路径题解
Denial of service DDoS Attacks
C语言：顺序存储结构的快速排序
PHP generates random numbers (nickname random generator)
Leetcode notes 566. Reshaping the matrix
[ecmascript6] symbol and its related use