Mysql practice questions 13.1

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Create a student table (student number, name, gender, age, major), and insert some data

Create a course table (course number, course name), insert department data

Create an elective form (student number, course number, grades), and insert part of the data. Complete the following query:

First create a database to establish three tables

mysql> create table students(
    -> id int(3),
    -> name varchar(20),
    -> sex varchar(10),
    -> age int(3),
    -> major varchar(30)
    -> );
mysql> create table kecheng(
    -> kcid int(3),
    -> kcname varchar(30)
    -> );
mysql> create table xianxiu(
    -> id int(3),
    -> kcid int(3),
    -> result int(3)
    -> );

adding data

 insert into students(id,name,sex,age,major)
    -> values(1,'张三','男',18,'经济'),
    -> (2,'张四','男',19,'金融'),
    -> (3,'张五','男',18,'法学'),
    -> (4,'张六','女',18,'数学'),
    -> (5,'李四','女',18,'数学'),
    -> (6,'李五','女',20,'金融'),
	-> (7,'王五','男',18,'地理');
	
insert into kecheng(kcid,kcname)
    -> values(1,'食品加工'),
    -> (2,'机械加工'),
    -> (3,'计算机组装'),
    -> (4,'哲学'),
    -> (5,'刑法学');

insert into xianxiu(id,kcid,result)
    -> values(1,2,99),
    -> (2,2,98),
    -> (3,1,97),
    -> (4,3,99),
    -> (5,4,99),
    -> (6,null,null),
    -> (7,null,null);

1. Query the information of the selected students and their selected courses

select students.*,kecheng.* from students join kecheng join xianxiu on kecheng.kcid=xianxiu.kcid and students.id=xianxiu.id;

2. Query the information of students who have selected courses and their selected courses and students who have not selected courses

>select students.*,kecheng.* from students left join xianxiu on students.id=xianxiu.id left join kecheng on xianxiu.kcid=kecheng.kcid

3. Information about students who choose courses and their selected courses and courses not selected by students

>select students.*,kecheng.* from students right join xianxiu on students.id=xianxiu.id right join kecheng on xianxiu.kcid=kecheng.kcid;

4. Query all the information in steps 2 and 3

>select students.*,kecheng.* from students left join xianxiu on students.id=xianxiu.id left join kecheng on xianxiu.kcid=kecheng.kcid
>union
>select students.*,kecheng.* from students right join xianxiu on students.id=xianxiu.id right join kecheng on xianxiu.kcid=kecheng.kcid;

5. Query the course information of the course number 1 and the student ID of the student who chose the course

elect kecheng.kcid,kecheng.kcname,students.id from students join kecheng join xianxiu on kecheng.kcid=xianxiu.kcid and students.id=xianxiu.id where xianxiu.kcid=1;

Mysql practice questions 13.1

Mysql practice questions 13.1

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