数据存储 | MySQL —— MySQL命令练习题(持续更新！)

1.表结构

2.建库/建表

• 建库

create database test default charset utf8;

• 创建class表 / 插入数据

-- 创建表
create table class (
  cid int not null auto_increment primary key,
  caption char(12) not null,
  unique uq_cp(caption)
) engine=innodb auto_increment=1 default charset=utf8;

-- 插入数据（多插入一些数据）
insert into class(caption)
values
("三年二班"),("一年三班"),("三年一班"),("三年三班"),("一年一班"),("一年二班");

• 创建teacher表 / 插入数据

-- 建表
create table teacher(
  tid int not null auto_increment primary key,
  tname varchar(24) not null
) engine=innodb auto_increment=1 default charset=utf8;

-- 插入数据（多插入一些数据）
insert into teacher(tname)
values
("赵老师"),("钱老师"),("孙老师"),("李老师"),("周老师"),("马老师"),("王老师");

• 创建student表 / 插入数据

-- 建表
create table student(
  sid int not null auto_increment primary key,
  gender char(3) not null,
  sname varchar(24) not null,
  class_id int,
  constraint foreign key fk_std_cls (class_id) references class (cid)
) engine=innodb auto_increment=1 default charset=utf8;

-- 插入数据（多插入一些数据）
insert into student(gender, sname, class_id)
values
("狗蛋","女","1"),("钢蛋","女","2"),("小名","男","3"),("小张","男","4"),
("小花","女","5"),("张三","男","6"),("马力","女","1"),("王五","女","2"),
("小孙","男","3"),("李三","男","4"),("周五","女","5"),("张爽","女","6");

• 创建course表 / 插入数据

-- 建表
create table course(
  cid int not null auto_increment primary key,
  cname varchar(24) not null,
  teacher_id int,
  constraint foreign key fk_cs_th (teacher_id) references teacher (tid)
) engine=innodb auto_increment=1 default charset=utf8;

-- 插入数据（多插入一些数据）
insert into course(cname, teacher_id)
values
("数据库原理","1"),("系统分析与设计","2"),("会计学","3"),("商务智能","4"),("机器学习","5"),("R语言","6"),
("Python","7"),("Linux","1"),("微机原理","3"),("管理学","3"),("科技论文写作","1");

• 创建score表 / 插入数据

-- 建表
create table score(
  sid int not null auto_increment primary key,
  student_id int,
  course_id int,
  number tinyint,
  constraint foreign key fk_sc_cs (course_id) references course (cid),
  constraint foreign key fk_sc_st (student_id) references student (sid),
  unique uq_st_cs (student_id, course_id)
) engine=innodb auto_increment=1 default charset=utf8;

-- 插入数据（多插入一些数据）
insert into score(student_id, course_id, number)
values
(1,1,10),(2,1,20),(3,1,60),(4,1,70),(5,1,80),(6,2,100),(7,2,50),(1,2,20),(2,2,98),(3,2,88),(4,3,79),(9,3,90),(11,3,95),(1,3,6),(2,3,100),(3,4,11),(4,5,0),(1,6,21),(2,7,60),(5,8,71),(3,9,95),(1,4,61),(1,5,88),(1,7,99),(1,8,42),(1,9,78),(1,10,88),(1,11,82);

3.操作表

• 1、自行创建测试数据

-- 参照上一小节

• 2、查询“数据库原理”课程比“会计学”课程成绩高的所有学生的学号

-- SQL语句
select A.student_id
from
(select score.student_id, score.number, course.cname
from score left join course on score.course_id=course.cid
where course.cname='数据库原理') as A
left join
(select score.student_id, score.number, course.cname
from score left join course on score.course_id=course.cid
where course.cname='会计学') as B on A.student_id=B.student_id
where A.number > B.number;

• 3、查询平均成绩大于60分的同学的学号和平均成绩； 

-- SQL语句
select score.student_id, avg(number) as avg
from score left join student on score.student_id=student.sid
group by score.student_id
having avg > 60;

•  4、查询所有同学的学号、姓名、选课数、总成绩；

-- SQL语句
-- [注意] ：此处是所有同学
select student.sid,student.sname,ifnull(count(score.number), 0),ifnull(sum(score.number),0)
from student left join score on student.sid=score.student_id
group by student.sid;

•  5、查询姓“李”的老师的个数；

-- SQL语句
select count(1)
from teacher
where tname like '李%';

• 6、查询没学过“赵”老师课的同学的学号、姓名；

-- SQL语句
select score.student_id, student.sname

from score left join course on score.course_id=course.cid
left join student on score.student_id=student.sid

where score.course_id in (
  select cid
  from course left join teacher on course.teacher_id=teacher.tid
  where teacher.tname="赵老师"
)

group by score.student_id;

•  7、查询学过“1”并且也学过编号“2”课程的同学的学号、姓名；

-- SQL语句
select student.sid,student.sname
from student left join score on student.sid=score.student_id
where score.course_id=1 or score.course_id=2
group by student.sid;

-- 去重：除了用group by之外,还可以用distinct,但是效率较低

•  8、查询学过“赵老师”所教的所有课的同学的学号、姓名；

-- SQL语句
select score.student_id,student.sname,count(1)
from score left join student on score.student_id=student.sid

where score.course_id in (select course.cid from course left join teacher on course.teacher_id=teacher.tid where teacher.tname like '赵%')

group by score.student_id
having count(1)=(select count(1) from course left join teacher on course.teacher_id=teacher.tid where teacher.tname like '赵%');

•  9、查询课程编号“2”的成绩比课程编号“1”课程成绩高的所有同学的学号、姓名；

-- SQL语句
select *

from (select student_id,course_id,number from score where course_id=1) as A inner join (select student_id,course_id,number from score where course_id=2) as B on A.student_id=B.student_id

where A.number < B.number;

• 10、查询有课程成绩小于60分的同学的学号、姓名；

-- SQL语句
select score.student_id,student.sname
from score left join student on score.student_id=student.sid
where score.number < 60
group by score.student_id;

•  11、查询没有学全所有课的同学的学号、姓名；

-- SQL语句
select score.student_id,student.sname
from score left join student on score.student_id=student.sid

group by score.student_id
having count(1) < (select count(1) from course);

•  12、查询至少有一门课与学号为“3”的同学所学相同的同学的学号和姓名；

-- SQL语句
select score.student_id,student.sname
from score left join student on score.student_id=student.sid
where score.course_id in (select course_id from score where score.student_id=3) and score.student_id != 3
group by score.student_id;

•   13、查询至少学过学号为“1”同学所选课程中任意一门课的其他同学学号和姓名；

-- SQL语句
-- [说明]：至少与学生2学的课一样多，或者比他学的多
select score.student_id,student.sname
from score left join student on score.student_id=student.sid
where score.course_id in (select course_id from score where score.student_id=1) and score.student_id != 1
group by score.student_id
having count(1) = (select count(1) from score where score.student_id=1);

•   14、查询和“2”号的同学学习的课程完全相同的其他同学学号和姓名；

-- SQL语句
select score.student_id,student.sname
from score left join student on score.student_id=student.sid

where score.student_id in (
  select student_id
  from score
  where score.student_id != 2
  group by score.student_id
  having count(1)=(select count(1) from score where score.student_id=2)
)

group by student_id
having count(1)=(select count(1) from score where score.student_id=2);

•  15、删除学习“马老师”课的score表记录；

-- SQL语句
delete
from score
where course_id in (
  select course.cid
  from course left join teacher on course.teacher_id=teacher.tid
  where teacher.tname='马老师'
);

•  16、向score表中插入一些记录，这些记录要求符合以下条件：①没有上过编号“2”课程的同学学号；②插入“2”号课程的平均成绩； 

-- SQL语句
insert into score(student_id, course_id, number)

(
  select sid,2,(select avg(number) from score where score.course_id=2)
  from student
  where sid not in (select student_id from score where score.course_id=2)
);

-- [注意]:判断没上过2号课程同学的学号，应当先确定上过该课程同学的学号，然后再进行排除；如果过程反过来了，则会出错！

•  17、按平均成绩从低到高显示所有学生的“数据库原理”、“系统分析与设计”、“会计学”三门的课程成绩，按如下形式显示： 学生ID,数据库原理,系统分析与设计,会计学,有效课程数,有效平均分；

-- SQL语句
select 
  student_id,
  (
      select s2.number
      from score as s2 inner join course on s2.course_id=course.cid
      where s2.student_id=s1.student_id and course.cname="数据库原理"
  ) as db,
  (
      select s2.number
      from score as s2 inner join course on s2.course_id=course.cid
      where s2.student_id=s1.student_id and course.cname="系统分析与设计"
  ) as sys,
  (
      select s2.number
      from score as s2 inner join course on s2.course_id=course.cid
      where s2.student_id=s1.student_id and course.cname="会计学"
  ) as calc,
  count(1) as course_num,
  avg(s1.number) as avg

from score as s1
group by s1.student_id
order by avg desc;

•  18、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；

-- SQL语句
select course_id,max(number) as max,min(number) as min
from score
group by course_id;

•  19、按各科平均成绩从低到高和及格率的百分数从高到低排序；

-- SQL语句
select 
  course_id, 
  avg(number) as avg,
  sum(case when number > 60 then 1 else 0 end)/count(1) as percent

from score

group by course_id
order by avg desc;

-- [注意]：case when ... then ... else ... end --> (三目运算符)

•  20、课程平均分从高到低显示（现实任课老师）；

-- SQL语句
select score.course_id, avg(score.number) as avg, teacher.tname

from score left join course on score.course_id=course.cid
left join teacher on course.teacher_id=teacher.tid

group by score.course_id
order by avg desc;

•  21、查询各科成绩前三名的记录:(不考虑成绩并列情况) 

-- SQL语句
select 
  s1.course_id,
  (select number from score as s2 where s2.course_id=s1.course_id group by number order by number desc limit 0,1) as first_person,
  (select number from score as s2 where s2.course_id=s1.course_id group by number order by number desc limit 1,1) as second_person,
  (select number from score as s2 where s2.course_id=s1.course_id group by number order by number desc limit 2,1) as third_person

from score as s1
group by course_id;

•  22、查询每门课程被选修的学生数；

-- SQL语句
select course.cid, course.cname, count(1)
from course left join score on course.cid=score.course_id

group by course.cid;

•  23、查询出只选修了一门课程的全部学生的学号和姓名；

-- SQL语句
-- 方法一
select sid, sname
from student
where sid in (
    select student_id
    from score
    group by student_id
    having count(1)=1
);

-- 方法二
select student.sid,student.sname
from student left join score on student.sid=score.student_id

group by student.sid
having count(1)=1;

• 24、查询男生、女生的人数；

-- SQL语句
select gender,count(1)
from student

group by gender;

•  25、查询姓“张”的学生名单；

-- SQL语句
select sid,sname
from student
where sname like '张%';

•  26、查询同名同姓学生名单，并统计同名人数；

-- 由于原始数据库中没有同名同姓的人，故先插入一部分数据
insert into student(sname,gender,class_id)
(select sname,gender,class_id from student limit 0,2);

insert into student(sname,gender,class_id)
(select sname,gender,class_id from student limit 0,4);


-- SQL语句
select sname,count(1)
from student

group by sname
having count(1) >=2;

•  27、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，按课程号降序排列；

-- SQL语句
select course_id,course.cname,avg(number) as avg
from score left join course on score.course_id=course.cid

group by course_id
order by avg asc, course_id desc;

•  28、查询平均成绩大于85的所有学生的学号、姓名和平均成绩；

-- SQL语句
select student_id,student.sname,avg(number) as avg
from score left join student on score.student_id=student.sid

group by student_id
having avg > 85;

•  29、查询课程名称为“数据库原理”，且分数低于60的学生姓名和分数；

-- SQL语句
select student_id,student.sname,score.number
from score left join student on score.student_id=student.sid
where score.course_id=(select cid from course where cname='数据库原理') and number < 60;

•  30、查询课程编号为3且课程成绩在80分以上的学生的学号和姓名； 

-- SQL语句
select score.student_id,student.sname
from score left join student on score.student_id=student.sid
where course_id=3 and number>80;

•  31、求选了课程的学生人数

-- SQL语句
select count(s1.student_id) as course_count
from (
  select student_id
  from score
  group by student_id
) as s1;

•  32、查询选修“赵老师”所授课程的学生中，成绩最高的学生姓名及其成绩；

-- SQL语句
select student.sname,score.number
from score left join student on score.student_id=student.sid
where course_id in (
    select cid
    from course
    where teacher_id=(select tid from teacher where tname='赵老师')
)

order by number desc
limit 0,1;

• 33、查询各个课程及相应的选修人数(注意是全部课程)；

-- SQL语句
select course.cid,count(1)
from course left join score on course.cid=score.course_id

group by course.cid;

•  34、查询不同课程但成绩相同的学生的学号、课程号、学生成绩；

-- SQL语句
-- 使用笛卡尔积
select s1.student_id,s2.student_id,s1.course_id,s1.number
from score as s1, score as s2

where s1.course_id != s2.course_id and s1.number = s2.number;

•  35、查询每门课程成绩最好的前两名；

-- SQL语句
select 
    course_id,
     (select student_id from score as s2 where s2.course_id=s1.course_id order by number desc limit 0,1) as stu_id_first,
    (select number from score as s2 where s2.course_id=s1.course_id order by number desc limit 0,1) as stu_score_first,
    (select student_id from score as s2 where s2.course_id=s1.course_id order by number desc limit 1,1) as stu_id_second,
    (select number from score as s2 where s2.course_id=s1.course_id order by number desc limit 1,1) as stu_score_second
from score as s1
group by course_id;

•  36、检索至少选修两门课程的学生学号；

-- SQL语句
-- 此处博主额外显示了每个学生选修的课程数
select student_id,count(1)
from score

group by student_id
having count(1) >= 2;

• 37、查询全部学生都选修的课程的课程号和课程名；

-- 所有课程中没有一门课被全部学生选修，因此先插入一些数据
insert into score(student_id,course_id,number)
values
(6,1,10),(7,1,20),(8,1,30),(9,1,60),(10,1,77),(11,1,80),(12,1,91),(7,3,69),(8,3,49),(12,3,72),(10,3,59);



-- SQL语句
select s1.course_id
from(
    select course_id,count(1) as cut
    from score
    group by course_id
) as s1 left join course on s1.course_id=course.cid

where s1.cut=(
    select count(1)
    from student
);

•  38、查询没学过“孙老师”讲授的任一门课程的学生姓名；

-- SQL语句
-- 需要先查询选修过孙老师课程的学生的学号，然后再排除
-- 博主附带查询了学生的学号
select sid,sname
from student
where sid not in (
    select student_id
    from score left join course on score.course_id = course.cid
    where teacher_id = (select tid from teacher where tname='孙老师')
    group by student_id
);

•  39、查询两门以上不及格课程的同学的学号及其平均成绩；

-- SQL语句
select student_id,count(1) as count,avg(number) as avg
from score
where number < 60

group by student_id
having count > 2;

•  40、检索“4”号课程分数小于60，按分数降序排列的同学学号；

-- SQL语句
select course_id,student_id,number
from score
where course_id = 4 and number < 60

order by number desc;

• 41、删除“2”号同学的“1”号课程的成绩；

-- 先查询看是否有对应成绩
select *
from score
where student_id = 2 and course_id  =1;

-- SQL语句
delete
from score
where student_id = 2 and course_id = 1;

-- 确认一下是否已经删除
select *
from score
where student_id = 2 and course_id  =1;