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Series Columns: MySQL Database

Haha, this is the homework assigned by our teacher, I'm wondering whether to use it or not to post a blog?

Finally, I thought about it, and let's post it. Although it is very simple, it can be practiced for those friends who are just learning databases. Because there is no answer, I don't know if it is right or not. If anyone finds a mistake, please point it out.

topic:

Check the student number, class and name of each student

Find all information about the course

Query which professional classes are in the database

Query information about courses with more than 60 credit hours

Query the student number, name and date of birth of students born in 1986

Query the number of students and courses whose scores are above 80 for three assignments

Query the student number, name and major class of the student surnamed Zhang

Query the information of boys in grade 05

Query student IDs and course IDs without homework grades

Query the total score of homework 1 of the student whose student number is 0538

Query the number of students who have taken the K001 course

Query how many classes are in the database

Query the student number and the average score of homework 1, the average score of homework 2, and the average score of homework 3 for students who take three or more courses (including 3 courses)

It doesn't matter if the friends are 0 based, look at the following blog and then do the questions.

The latest MySQL foundation in 2022

1. Create a database

create database  if not exists  db2 ;

Ok, the creation is successful, then we open the console

2. Create the table

1. Create a student table

analyze:

Student ID: character type

name: character

gender: character type gender is a word so varchar(1)

Professional Class: Character Type

Date of birth: time type date

Contact phone number: character phone number with 11 digits varchar(11).

drop table if exists student;
create table student
(
    id     varchar(10) comment '学号',
    name   varchar(10) NOT NULL comment '姓名',
    gender char(1) comment '性别',
    class  varchar(20) comment '专业班级',
    date   date comment '出生日期',
    iphone varchar(11) comment '联系电话'
)
    comment '学生表';

select * from student;

2. Create a class schedule

drop table if exists student_course;
create table student_course
(
    course_id     varchar(10)  comment '课程号',
    course_name   varchar(15) comment '课程名',
    course_number double unsigned comment '学分数',
    student_time  int unsigned comment '学时数',
    teacher       varchar(10) comment '任课教师'
)
    comment '课程表';
select *
from student_course;

3. Student worksheet

drop table if exists student_homework;
create table student_homework
(
    course_id  varchar(10) comment '课程号',
    id      varchar(10)    comment '学号',
    homework_1 int comment '作业1成绩',
    homework_2 int comment '作业2成绩',
    homework_3 int comment '作业3成绩'

)
    comment '学生作业表';
select *
from student_homework;

3. Add data

Type them out one by one according to the data on the picture, woo woo woo

1. Student table

insert into student
values ('0433', '张艳', '女', '生物04', '1986-9-13', null),
       ('0496', '李越', '男', '电子04', '1984-2-23', '1381290xxxx'),
       ('0529', '赵欣', '男', '会计05', '1984-1-27', '1350222xxxx'),
       ('0531', '张志国', '男', '生物05', '1986-9-10', '1331256xxxx'),
       ('0538', '于兰兰', '女', '生物05', '1984-2-20', '1331200xxxx'),
       ('0591', '王丽丽', '女', '电子05', '1984-3-20', '1332080xxxx'),
       ('0592', '王海强', '男', '电子05', '1986-11-1', null);

Check it out:

select * from student;

2. Class Schedule

INSERT INTO student_course
values ('K001', '计算机图形学', 2.5, 40, '胡晶晶'),
       ('K002', '计算机应用基础', 3, 48, '任泉'),
       ('K006', '数据结构', 4, 64, '马跃先'),
       ('M001', '政治经济学', 4, 64, '孔繁新'),
       ('S001', '高等数学', 3, 48, '赵晓尘');

Check it out:

select *
from student_course;

3. Student worksheet

insert into student_homework values
('K001','0433',60,75,75),
('K001','0529',70,70,60),
('K001','0531',70,80,80),
('K001','0591',80,90,90),
('K002','0496',80,80,90),
('K002','0529',70,70,85),
('K002','0531',80,80,80),
('K002','0538',65,75,85),
('K002','0592',75,85,85),
('K006','0531',80,80,90),
('K006','0591',80,80,80),
('M001','0496',70,70,80),
('M001','0591',65,75,75),
('S001','0531',80,80,80),
('S001','0538',60,null,80);

Check it out:

select *
from student_homework;

4. Start doing questions

1. Check the student number, class and name of each student

select id,class,name from student;

2. Check all the information of the course

select *
from student_course;

3. Query which professional classes are in the database

select  class from student;

4. Inquire about course information with more than 60 credit hours

select course_id,course_name from student_course where student_time>60;

5. Query the student number, name and date of birth of students born in 1986

select id,name,date from student where date>=('1986-1-1') AND date<('1987-1-1');

6. Inquire about the student number and course number of the three homework scores above 80 points

At first I used this query again:
select * from student_homework where homework_1>80 and homework_2>80 and homework_3>80;
I found that there was nothing, so I looked at the data and found that there is no such data for three homework scores above 80.

Therefore, the question: "Inquiry about the student number and course number with a score of 80 or more in three assignments" should include 80 points

So, I modify it:
select * from student_homework where homework_1>=80 and homework_2>=80 and homework_3>=80;

7. Query the student number, name and major class of the student surnamed Zhang

Error example:

Since I haven't written SQL for hundreds of years, I actually wrote (slap myself):
select id,name,class from  student where name = '张%';

select id,name,class from  student where name like '张%';

8. Query the information of boys in grade 05

select * from student where class like '%05' and gender='男';

9. Query the student number and course number without homework grades

select id,course_id from student_homework where homework_1 is null or homework_2 is null or homework_3 is null ;

10. Query the total score of homework 1 of the student whose student number is 0538

select sum(homework_1) '总分' from student_homework where id='0538';

11. Query the number of students who have taken the K001 course as an elective

select count(*) from student_homework where course_id='K001';

12. Query how many classes are in the database

select count(*) from student where class is not null ;

13. Query the student number and the average score of Homework 1, the average score of Homework 2, and the average score of Homework 3 who have taken three or more courses (including 3 courses)

select student.id, avg(homework_1), avg(homework_2), avg(homework_3)
from student
         left join student_homework on student.id = student_homework.id
group by student.id
having count(course_id) >= 3;

MySQL small exercises (only suitable for beginners, non-beginners are not allowed to enter)

topic:

1. Create a database

2. Create the table

1. Create a student table

2. Create a class schedule

3. Student worksheet

3. Add data

4. Start doing questions

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