MySQL多表查询练习

二、多表查询
1.创建student和score表

create table student (
id int not null unique primary key,
name varchar(20) not null,
sex varchar(4),
birth year,
department varchar(20),
address varchar(50)
);

创建score表。SQL代码如下：

create table score (
id int not null unique primary key auto_increment,
stu_id int not null,
c_name varchar(20),
grade int(10)
);

2.为student表和score表增加记录
向student表插入记录的INSERT语句如下：

INSERT INTO student VALUES( 901,'张老大', '男',1985,'计算机系', '北京市海淀区');
INSERT INTO student VALUES( 902,'张老二', '男',1986,'中文系', '北京市昌平区');
INSERT INTO student VALUES( 903,'张三', '女',1990,'中文系', '湖南省永州市');
INSERT INTO student VALUES( 904,'李四', '男',1990,'英语系', '辽宁省阜新市');
INSERT INTO student VALUES( 905,'王五', '女',1991,'英语系', '福建省厦门市');
INSERT INTO student VALUES( 906,'王六', '男',1988,'计算机系', '湖南省衡阳市');

向score表插入记录的INSERT语句如下：
 

INSERT INTO score VALUES(NULL,901, '计算机',98);
INSERT INTO score VALUES(NULL,901, '英语', 80);
INSERT INTO score VALUES(NULL,902, '计算机',65);
INSERT INTO score VALUES(NULL,902, '中文',88);
INSERT INTO score VALUES(NULL,903, '中文',95);
INSERT INTO score VALUES(NULL,904, '计算机',70);
INSERT INTO score VALUES(NULL,904, '英语',92);
INSERT INTO score VALUES(NULL,905, '英语',94);
INSERT INTO score VALUES(NULL,906, '计算机',90);
INSERT INTO score VALUES(NULL,906, '英语',85);

1.查询student表的所有记录

select * from student;

2.查询student表的第2条到4条记录

select * from student limit 1,3;

3.从student表查询所有学生的学号（id）、姓名（name）和院系（department）的信息

select id,name,department from student;

4.从student表中查询计算机系和英语系的学生的信息

select * from student where department in ('计算机系','英语系');

5.从student表中查询年龄18~22岁的学生信息

select * from student where (2023-birth) between 18 and 22;

6.从student表中查询每个院系有多少人

select department,count(*) as '总人数' from student group by department;

7.从score表中查询每个科目的最高分

select c_name ,max(grade) as '最高分'  from score group by c_name;

8.查询李四的考试科目（c_name）和考试成绩（grade）

select name,c_name,grade from student,score where student.id=score.stu_id having name='李四';

9.用连接的方式查询所有学生的信息和考试信息

select student.*,c_name,grade from student inner join score on student.id=score.stu_id;

10.计算每个学生的总成绩

select name,sum(grade) as '总成绩' from student inner join score on student.id=score.stu_id group by name;

11.计算每个考试科目的平均成绩

select c_name,avg(grade) from score group by c_name;

12.查询计算机成绩低于95的学生信息

select student.*,c_name,grade from student inner join score on student.id=score.stu_id having c_name='计算机' and grade<95;

13.查询同时参加计算机和英语考试的学生的信息

select * from student  where id in (select stu_id from score where c_name='计算机 ') and id in (select stu_id from score where c_name='英语');


14.将计算机考试成绩按从高到低进行排序

select c_name , grade from score where c_name = '计算机' order by grade desc;

15.从student表和score表中查询出学生的学号，然后合并查询结果

select id from student union select stu_id from score;

16.查询姓张或者姓王的同学的姓名、院系和考试科目及成绩

select name,department,c_name,grade from student inner join score on student.id=score.stu_id having name like '张%' or name like '王%';

17.查询都是湖南的学生的姓名、年龄、院系和考试科目及成绩

select name,(2023 - birth) as age,department,c_name,grade from student inner join score on student.id=score.stu_id where address regexp '^湖南省';