前言
大家好，分享一些MySQL练习题，都是自己整理的考试例题附有答案，可用作巩固知识点，也可以用来考前复习。
一、创建数据库
1.创建一个叫做Mytest 的数据库，在该库中建立以下5张表，表之间的关系及字段如图所示：
创建数据库：
create database Mytest;
创建teacher表：
create table teacher(
id smallint(4) not null primary key,
name varchar(20)
);
创建class表：
create table class(
id smallint(6) not null primary key,
name varchar(50)
);
创建course表
create table course(
id smallint(3) not null primary key,
name varchar(100),
teacher_id smallint(6) not null,
foreign key(teacher_id) references teacher(id)
);
创建student表
create table student(
id smallint(6) not null primary key,
name varchar(20),
gender char(2),
class_id smallint(6) not null,
foreign key(class_id) references class(id)
);
创建score表
create table score(
id int(11),
student_id smallint(6) not null,
course_id smallint(3) not null,
mark tinyint(4),
foreign key(student_id) references student(id),
foreign key(course_id) references course(id),
primary key(student_id,course_id)
);
2.插入下图数据
有两种方式插入数据（演示两表）：
1.单行插入
例：插入class表数据
insert into class values(1,"软件工程1班");
insert into class values(2,"计算机科学技术1班");
insert into class values(3,"网络工程1班");
2,。批量插入
例：插入teacher表数据
insert into teacher values
(1,"老虎"),
(2,"小马"),
(3,"大牛");
二、操作数据库
1.查询所有的课程的名称以及对应的任课老师姓名；
select course.name,teacher.name
from course inner join teacher
on course.teacher_id = teacher.id;
2.查询学习课程"数据结构"比课程"java语言"成绩低的学生的学号；
select shuju.student_id from
(select score.student_id,course.name,score.mark from
score inner join course on
score.course_id=course.id where
course.name="数据结构") as shuju
inner JOIN
(select score.student_id,course.name,score.mark from
score inner join course on
score.course_id=course.id where
course.name="java语言") as java
on shuju.student_id=java.student_id
where shuju .mark<java.mark;
3 查询平均成绩大于65分的同学的id和平均成绩(保留两位小数)；
select student_id,round(avg(mark),2) as grade from score
group by student_id having grade>65;
4. 查询平均成绩大于65分的同学的姓名和平均成绩(保留两位小数)；
select student.name,round(avg(mark),2)
as grade from score
inner joinstudent
onscore.student_id=student.id
group by student_id having grade>65;
5. 查询所有同学的姓名、选课数、总成绩；
select student.name,count(score.course_id)
as "选课数",sum(score.mark) as "总成绩" from score
inner join student on score.student_id=student.id
group by student_id;
6. 查询没学过"大牛"老师课的同学的姓名；
select name from student
where id not in(select id from score where course_id in(3,3));
7. 查询学过"大牛"老师所教的全部课程的同学的姓名；
select student.name from
score inner join student
on score.student_id=student.id where score.course_id in
(select course.id from course inner join teacher
on course.teacher_id=teacher.id where teacher.name="大牛")
group by score.student_id;
8. 查询有课程成绩小于60分的同学的姓名；
select name from student where id in
(select student_id from score where mark<60
group by student_id);
9. 查询选修了全部课程的学生姓名；
select name from student where id in
(select student_id from score
group by student_id
having count(1)=(select count(1) from course));
10. 查询至少有一门课程与"小草"同学所学课程相同的同学姓名；
select name as"姓名" from
student where id in
(select student_id from score where course_id in
(select course_id from score
inner join student
on score.student_id=student.id where student.name="小草")
group by student_id)
and name!="小草";
11. 查询至少有一门课程和"小草"同学所学课程不相同的同学姓名；
select name as "姓名" from student where id in
(select student_id from score where course_id in
(select course_id from score
inner join student
on score.student_id!=student.id
where student.name="小草")
group by student_id)
and name!="小草";
12. 查询各科成绩最高和最低的分：以如下形式显示：课程id，最高分，最低分；
select course_id as "课程id",
max(mark) as "最高分",
min(mark) as "最低分"
from score group by course_id;
13. 查询只选修了一门课程的学生的学号和姓名；
select
student_id as"学生学号",
student.name as"学生姓名" from score
inner join student
on score.student_id=student.id
group by student_id
having count(course_id)=1;
14. 查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程id降序排列。
select course.name as"课程名称",
avg(mark) as"平均成绩" from score
inner join course
on score.course_id=course.id
group by course_id
order by avg(mark) asc,
course_id desc;
15. 按平均成绩倒序显示所有学生的"数据库原理"、“java语言”、"C语言"三门的课程成绩，按如下形式显示： 学生id、数据库原理、java语言、C语言、课程数、平均分；(高级应用较难)
- 先查询单一学生的数据库原理课程分数
select mark as"分数" from score
left join course
on score.course_id = course.id
where course.name = "数据库原理" and score.student_id=1;
- 将上面查询的结果作为列字段使用，得到最终结果
select student_id as"学生学号",
(select mark from score
left join course
on score.course_id = course.id
where course.name = "数据库原理"
and score.student_id=sc.student_id)
as "数据库原理",
(select mark from score
left join course
on score.course_id = course.id
where course.name = "java语言"
and score.student_id=sc.student_id)
as "java语言",
(select mark from score
left join course
on score.course_id = course.id
where course.name = "C语言"
and score.student_id=sc.student_id)
as "C语言",
count(course_id) as "课程数",
avg(mark) as "平均分"
from score as sc
group by student_id
order by avg(mark) desc;