MySQL经典45题

练习数据

数据表

–1.学生表 Student(SId,Sname,Sage,Ssex)–SId 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别

–2.课程表 Course(CId,Cname,TId) --CId --课程编号,Cname 课程名称,TId 教师编号

–3.教师表 Teacher(TId,Tname) --TId 教师编号,Tname 教师姓名

–4.成绩表 SC(SId,CId,score) --SId 学生编号,CId 课程编号,score 分数

创建测试数据

学生表Student

create table Student(SId varchar(10),Sname varchar(10),Sage datetime,Ssex varchar(10));
insert into Student values('01' , '赵雷' , '1990-01-01' , '男');
insert into Student values('02' , '钱电' , '1990-12-21' , '男');
insert into Student values('03' , '孙风' , '1990-05-20' , '男');
insert into Student values('04' , '李云' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-03-01' , '女');
insert into Student values('07' , '郑竹' , '1989-07-01' , '女');
insert into Student values('09' , '张三' , '2017-12-20' , '女');
insert into Student values('10' , '李四' , '2017-12-25' , '女');
insert into Student values('11' , '李四' , '2017-12-30' , '女');
insert into Student values('12' , '赵六' , '2017-01-01' , '女');
insert into Student values('13' , '孙七' , '2018-01-01' , '女');

课程表Course

create table Course(CId varchar(10),Cname varchar(10),TId varchar(10));
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');

教师表 Teacher

create table Teacher(TId varchar(10),Tname varchar(10));
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');

成绩表 SC

create table SC(SId varchar(10),CId varchar(10),score decimal(18,1));
insert into SC values('01' , '01' , 80);
insert into SC values('01' , '02' , 90);
insert into SC values('01' , '03' , 99);
insert into SC values('02' , '01' , 70);
insert into SC values('02' , '02' , 60);
insert into SC values('02' , '03' , 80);
insert into SC values('03' , '01' , 80);
insert into SC values('03' , '02' , 80);
insert into SC values('03' , '03' , 80);
insert into SC values('04' , '01' , 50);
insert into SC values('04' , '02' , 30);
insert into SC values('04' , '03' , 20);
insert into SC values('05' , '01' , 76);
insert into SC values('05' , '02' , 87);
insert into SC values('06' , '01' , 31);
insert into SC values('06' , '03' , 34);
insert into SC values('07' , '02' , 89);
insert into SC values('07' , '03' , 98);

练习题目

1. 查询" 01 “课程比” 02 "课程成绩高的学生的信息及课程分数

   1.1 查询同时存在" 01 “课程和” 02 "课程的情况

   1.2 查询存在" 01 “课程但可能不存在” 02 "课程的情况(不存在时显示为 null )

   1.3 查询不存在" 01 “课程但存在” 02 "课程的情况

   select a.*,b.cid,b.score
   from sc a inner join sc b
   where a.sid=b.SId and a.CId='01'and b.CId='02' and a.score>b.score;
   #1.1
   select a.sid,a.score,b.sid,b.score
   from sc a inner join sc b
   where a.sid=b.sid and a.CId='01'and b.CId='02'
   #1.2
   select a.*,b.cid,b.score
   from (select * from sc where cid='01' )a left join (select * from sc where cid='02') b
   on a.sid=b.sid
   #1.3
   select *
   from sc 
   where sc.cid not in (select cid from sc where cid='01')
   and sc.cid='02'
   

2. 查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩

   select student.sid,student.sname,a.avg_score
   from  student 
   inner join(
   	select sc.sid,avg(score) avg_score
   	from sc
   	GROUP BY sc.sid
   	HAVING avg(sc.score)>=60)a 
   on a.SId=student.sid
   

3. 查询在 SC 表存在成绩的学生信息

   select b.*
   from
   (select sid
   from sc 
   GROUP BY sid) a
   INNER  JOIN student b
   on a.sid=b.sid
   

   group by 只能查询分组字段，其它字段只能以聚合函数的形式被查询出来

4. 查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为 null )

   4.1 查有成绩的学生信息

   select 
   a.sid,
   a.sname,
   count(b.cid) as counts,
   sum(b.score) as sum_score
   from 
   student a LEFT JOIN sc b
   on a.sid=b.sid
   GROUP BY a.sid
   #4.1
   
   

5. 查询「李」姓老师的数量

   select count(*) from teacher
   where tname LIKE '李%'
   

6. 查询学过「张三」老师授课的同学的信息

   select * from course a inner join teacher b on a.tid=b.tid;
   
   select * from sc a inner join (select a.*,b.tname from course a inner join teacher b on a.tid=b.tid)b on a.cid=b.cid;
   
   select a.*,b.tname from student a inner join (select a.*,b.tname from sc a inner join (select a.*,b.tname from course a inner join teacher b on a.tid=b.tid)b on a.cid=b.cid)b on a.sid=b.sid having b.tname='张三';
   

7. 查询没有学全所有课程的同学的信息

   select b.*
   from sc a
   inner join student b
   on a.sid=b.sid
   group by a.sid
   having count(1)<(select count(1) from course)
   

8. 查询至少有一门课与学号为" 01 "的同学所学相同的同学的信息

   select a.* from student a right join(
   select sid from sc where cid in(select cid
   from sc 
   where sid='01'))b
   on a.sid=b.sid
   group by a.sid
   having a.sid != '01'
   
   

9. 查询和" 01 "号的同学学习的课程 完全相同的其他同学的信息

   select b.*
   from (select * from sc where sid not in (select sid from sc where cid not in (select cid from sc where sid='01')))a
   left join student b
   on a.sid=b.sid
   group by a.sid
   having count(cid)=(select count(1) from sc where sid='01');
   

10. 查询没学过"张三"老师讲授的任一门课程的学生姓名

    select * from student where sid not in
    (select c.sid from teacher a right join course b
    on a.tid=b.tid
    right join sc c
    on c.cid= b.cid
    where tname='张三')
    

11. 查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩

    select sc.sid, sname ,avg(score) avg_score
    from sc left join student 
    on sc.sid=student.sid 
    where score<60 
    group by sid 
    having count(1)>1
    

12. 检索" 01 "课程分数小于 60，按分数降序排列的学生信息

    select score,b.* from
    sc a left join student b
    on a.sid=b.sid where a.cid='01' and score<60 group by a.sid
    order by score desc
    

13. 按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩

    select a.* ,avg_score from 
    sc a left join (select avg(score) avg_score,sid from sc group by sid )b
    on a.sid=b.sid
    order by avg_score desc
    

14. 查询各科成绩最高分、最低分和平均分： 以如下形式显示：课程 ID，课程 name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率 及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90 要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列

    #sum(case when score>=60 then 1 else 0 end)/count(1) as 及格率
    #sum(case when score>=70 and score<80 then 1 else 0 end)/count(1) as 中等率
    #sum(case when score>=80 and score<90 then 1 else 0 end)/count(1) as 优良率
    #sum(case when score>=90  then 1 else 0 end)/count(1) as 优秀率
    select sc.cid '课程ID',cname '课程name',max(score) '最高分',min(score) '最低分',avg(score) '平均分',count(1) '选修人数',sum(case when score>=60 then 1 else 0 end)/count(1) '及格率',sum(case when score>=70 and score<80 then 1 else 0 end)/count(1) '中等率',sum(case when score>=80 and score<90 then 1 else 0 end)/count(1) '优良率',sum(case when score>=90  then 1 else 0 end)/count(1) '优秀率'
     from sc left join course
     on sc.cid=course.cid
     group by sc.cid
     order by count(1) desc ,sc.cid asc
    

15. 按各科成绩进行排序，并显示排名， Score 重复时保留名次空缺

    select @rank:= 1;
    select @rank;

    15.1 按各科成绩进行排序，并显示排名， Score 重复时合并名次

    select sid,cid,score,
    @rank:=@rank+1 as rn
    from sc,(select @rank:=0) t
    order by score desc
    #15.1
    select sid,cid,score,
    case when @sco=score then @rank
    		 when @sco:=score then @rank:=@rank+1 end as rn
    from sc,(select @rank:=0,@sco:=null) t
    order by score desc
    

16. 查询学生的总成绩，并进行排名，总分重复时保留名次空缺

    16.1 查询学生的总成绩，并进行排名，总分重复时不保留名次空缺

    select a.*,
    @rank:=@rank+1
    from
    (select sid,sum(score) scos from sc group by sid order by scos desc)a,(select @rank:=0)b
    #16.1
    select 
    a.sid,
    @rank:=if(@sco=scos,'',@rank+1) as rank,
    @sco:=scos
    from
    (select sid,sum(score) scos from sc group by sid order by scos desc) a,
    (select @sco:=null,@rank:=0)b
    

17. 统计各科成绩各分数段人数：课程编号，课程名称，[100-85]，[85-70]，[70-60]，[60-0] 及所占百分比

    select sc.cid,cname,
    concat(sum(case when 0

18. 查询各科成绩前三名的记录

    select 
    a.*
    from sc a
    where 
    (select count(1) from sc b where b.cid=a.cid and b.score>a.score)<3
    order by cid desc,score desc
    

19. 查询每门课程被选修的学生数

    select cid,count(1)
    from sc
    group by cid
    

20. 查询出只选修两门课程的学生学号和姓名

    select a.sid,b.sname
    from sc a left join student b
    on a.sid=b.sid
    group by a.sid,b.sname
    having count(1)=2
    

21. 查询男生、女生人数

    select ssex,count(1) as counts
    from student
    GROUP BY ssex
    

22. 查询名字中含有「风」字的学生信息

    select *
    from student
    where sname like '%风%'
    

23. 查询同名同性学生名单，并统计同名人数

    #提示：自关联
    select a.sname,a.ssex,count(1) as conts
    from student a inner join student b
    on a.sname=b.sname and a.ssex=b.ssex and a.sid!=b.sid
    group by a.sname,a.ssex
    

24. 查询 1990 年出生的学生名单

    #使用year函数
    select *
    from student
    where year(sage)=1990
    

25. 查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列

    select avg(score),sid
    from sc
    group by sid
    order by avg(score) desc,sid asc
    

26. 查询平均成绩大于等于 85 的所有学生的学号、姓名和平均成绩

    select a.sid,b.sname,avg(score)
    from sc a inner join student b on a.sid=b.sid 
    group by a.sid
    having avg(score)>85
    

27. 查询课程名称为「数学」，且分数低于 60 的学生姓名和分数

    select b.score ,sname
    from student a right join
    (select score,sid from sc a inner join course b on a.cid=b.cid
    where  score<60 and cname='数学')b
    on b.sid=a.sid
    

28. 查询所有学生的课程及分数情况（存在学生没成绩，没选课的情况）

    select sname,cname,score
    from student a left join 
    (select sid,score,cname
    from sc a left join course b
    on a.cid=b.cid) b
    on a.sid=b.sid
    
    

29. 查询任何一门课程成绩在 70 分以上的姓名、课程名称和分数

    select sname,cname,score
    from 
    (select sid,score,cname from sc a left join course b
    on a.cid=b.cid) a left join student b
    on a.sid=b.sid 
    where score>70
    
    
    select sname,cname,score
    from sc a left join course b
    on a.cid=b.cid
    left join student c
    on a.sid=c.sid 
    where score>70
    

30. 查询不及格的课程

    select a.*,cname from sc a left join course b
    on a.cid=b.cid
    where score<60
    

31. 查询课程编号为 01 且课程成绩在 80 分以上的学生的学号和姓名

    select sc.sid,sname
    from sc left join student
    on sc.sid=student.sid
    where cid='01' and score>80
    

32. 求每门课程的学生人数

    select cid, count(1) as counts from sc group by cid;
    

33. 成绩不重复，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩

    select b.*,a.score
    from sc a left join student b
    on a.sid=b.sid
    left join course c
    on a.cid=c.cid
    left join teacher d
    on c.tid=d.tid
    where d.tname='张三'
    order by a.score desc limit 1
    

34. 成绩有重复的情况下，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩

    select s.*
    from (
    select a.*,
    case when @sco = score then @rank
    		 when @sco:=score then @rank:=@rank+1 end as rn
    from 
    (select b.*,score
    from sc a left join student b
    on a.sid=b.sid
    left join course c
    on a.cid=c.cid
    left join teacher d
    on c.tid=d.tid
    where d.tname='张三') a,(select @sco:=null,@rank:=0)b)s
    where rn=1
    

35. 查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩

    select 
    a.sid,a.cid
    from sc a inner join sc b on a.sid=b.sid
    where a.cid!=b.cid and a.score=b.score
    group by a.sid,a.cid
    

36. 查询每门功成绩最好的前两名

    select s.cid,s.score,s.sid
    from 
    (select 
    sc.*,
    @rank:=if(@c_cid=cid,if(@sco=score,@rank,@rank+1),1) as rank,
    @sco:=score,
    @c_cid:=cid
    from sc,(select @sco:=null,@rank:=0,@c_cid:=null)b
    order by cid,score desc)s
    where rank<=2
    

37. 统计每门课程的学生选修人数（超过 5 人的课程才统计）。

    select cid,count(1)
    from sc 
    group by cid
    having count(1)>5
    

38. 检索至少选修两门课程的学生学号

    select sid, count(1) from sc
    group by sid
    having count(1)>=2
    

39. 查询选修了全部课程的学生信息

    select student.* from sc inner join student
    on sc.sid=student.sid
    group by sc.sid
    having count(1)=(select count(1) from course )
    

40. 查询各学生的年龄，只按年份来算

    #now(),curdate()
    select sname,year(now())-year(sage) age from student
    

41. 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一

    select sname,timestampdiff(year,sage,now())as age from student;
    

42. 查询本周过生日的学生

    select *,week(sage),
    week(now())
    from student where week(sage)=week(now());
    

43. 查询下周过生日的学生

    select *,week(sage),
    week(now())
    from student where week(sage)=week(now())+1;
    

44. 查询本月过生日的学生

    select *,month(sage),
    month(now())
    from student where month(sage)=month(now());
    

45. 查询下月过生日的学生

    select *,month(sage),
    month(now())
    from student where month(sage)=month(now())+1;