MYSQL45道练习题

表：Student

 表：SC

 表：Course

 表：Teacher

1.查询" 01 "课程比" 02 "课程成绩高的学生的信息及课程分数

select a.sid,c.Sname,c.Sage,c.Ssex,a.score_01,b.score_02
from
   -- 选出课程号为01的学生及成绩信息
   (select SId,score as score_01
    from SC
    where CId='01') as a
   INNER JOIN
     -- 选出课程号为02的学生及成绩信息
   (select SId,score as score_02
    from SC
    where CId='02') as b
   on a.SId=b.SId
   INNER JOIN Student as c
   ON a.SId=c.SId
where a.score_01 > b.score_02

-1.1 查询同时存在" 01 "课程和" 02 "课程的情况

select a.sid,c.Sname,c.Sage,c.Ssex,a.score_01,b.score_02
from
   -- 选出课程号为01的学生及成绩信息
   (select SId,score as score_01
    from SC
    where CId='01') as a
   INNER JOIN
     -- 选出课程号为02的学生及成绩信息
   (select SId,score as score_02
    from SC
    where CId='02') as b
   on a.SId=b.SId
   INNER JOIN Student as c
   ON a.SId=c.SId

-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 )

select a.sid,c.Sname,c.Sage,c.Ssex,a.score_01,b.score_02
from
   -- 选出课程号为01的学生及成绩信息
   (select SId,score as score_01
    from SC
    where CId='01') as a
   LEFT JOIN
     -- 选出课程号为02的学生及成绩信息
   (select SId,score as score_02
    from SC
    where CId='02') as b
   on a.SId=b.SId
   INNER JOIN Student as c
   ON a.SId=c.SId

-1.3 查询不存在" 01 "课程但存在" 02 "课程的情况

select *
from SC as a
where SId not in (select SId from SC where CId='01')  
      and 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 a.sid,b.sname,avg(score) as avg_score
from SC as a
INNER JOIN Student as b
on a.SId=b.SId
group by a.SId,b.Sname

3.查询在 SC 表存在成绩的学生信息

select *
from Student
where SId in (select DISTINCT SId from SC)

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 ) 

select a.SId,a.Sname,count(b.CId),sum(b.score)
from Student as a
LEFT JOIN SC as b
on a.SId=b.SId
GROUP BY a.SId,a.Sname

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 Student
where sid in(select sid
             from SC
             where cid in(select cid
                          from Course
                          where tid in(select TId
                                       from Teacher
                                       where tname='张三')))

7.查询没有学全所有课程的同学的信息

select a.SId,a.Sname,a.Sage,a.Ssex,count(b.CId)
from Student as a
LEFT JOIN SC as b on a.SId=b.SId
group by a.SId,a.Sname,a.Sage,a.Ssex
having count(b.CId)<(select count(CId) 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 *
from Student as a 
INNER JOIN (select distinct sid
            from SC
            where cid in (select cid
                          from SC
                          where sid='01')) as b
on a.SId=b.SId
-- inner join处理效率比where in高

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 * 
from Student
-- 选出和01同学选课数量相同的同学
WHERE SId in (select SId
              from SC
              group by SId having count(CId)=(select count(CId) 
                                              from SC 
                                              where SId='01'))
-- 排除选了01同学所选课程以外课程的同学
      and SId not in(select DISTINCT SId
                     from SC
                     where CId not in (SELECT CId
                                       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 Sname
from Student
where sid not in(select sid
                 from SC
                 where cid in(select cid
                              from Course
                              where tid in(select TId
                                           from Teacher
                                           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 a.SId,a.Sname,avg(score)
from Student as a
right join SC as b
on a.SId=b.SId
group by a.SId,a.Sname having a.sid in(select SId
                                       from SC
                                       where SC.score<60
                                       group by SId having count(SId)>=2)

12.检索" 01 "课程分数小于 60，按分数降序排列的学生信息

select *
from SC as a
left join Student as b
on a.SId=b.SId
where a.CId='01' and a.score<60
order by a.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 c.SId,a.CId,a.score,b.avg_score
from SC as a
left join (select SId,avg(score) as avg_score
           from SC
           group by SId) as b
on a.SId=b.SId
right join Student as c
on a.SId=c.SId
order by b.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

-- 用if函数来做
select a.CId as '课程ID',
       b.Cname as '课程name',
       max(a.score) as '最高分',
       min(a.score) as '最低分',
       avg(a.score) as '平均分',
       sum(if(a.score>=60,1,0))/count(a.score) as '及格率',
       sum(if(a.score>=70 and a.score<=80,1,0))/count(a.score) as '中等率',
       sum(if(a.score>=80 and a.score<=90,1,0))/count(a.score) as '优良率',
       sum(if(a.score>=90,1,0))/count(a.score) as '优秀率'
from SC as a
join Course as b on a.CId=b.CId
group by a.CId,b.Cname

-- 用case when来做
select a.CId as '课程ID',
       b.Cname as '课程name',
       max(a.score) as '最高分',
       min(a.score) as '最低分',
       avg(a.score) as '平均分',
       sum(case when a.score>=60 then 1 else 0 end)/count(a.score) as '及格率',
       sum(case when a.score>=70 and a.score<=80 then 1 else 0 end)/count(a.score) as '中等率',
       sum(case when a.score>=80 and a.score<=90 then 1 else 0 end)/count(a.score) as '优良率',
       sum(case when a.score>=90 then 1 else 0 end)/count(a.score) as '优秀率'
from SC as a
join Course as b on a.CId=b.CId
group by a.CId,b.Cname

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 

-- @rank:=是赋值函数
select SId,CId,score,@rank:=@rank+1 as rn
from SC,(select @rank:=0) as t
order by score desc

-- 窗口函数row_number（）可以对数据进行排序
select *,
       row_number() over(order by score desc) as 'rank'
from sc

15.1 按各科成绩进行排序，并显示排名， Score 重复时合并名次

-- 加入@sco判断本行分数与上一行是否相同
-- 保留@sco的写法
select SId,
       CId,
       score,
       case when @sco=score then @rank else @rank:=@rank+1 end as rn,
       @sco:=score
from SC,(select @rank:=0,@sco:=null) as t
order by score desc

-- 隐藏@sco的写法
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) as t
order by score desc

-- 窗口函数rank，可以对相同的分数输出同样的排名，总名次不变，排名是跳跃的
select *,
       rank() over(order by score desc) as 'rank'
from sc

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 

-- 保留@sco的写法
select s.*,
       @rank:=if(@sco=s_sco,'',@rank+1) as rn,
       @sco:=s_sco
from (select SId,
      sum(score) as s_sco
      from SC
      group by SId
      order by s_sco desc) as s,
     (select @rank:=0,@sco:=null) as t

-- 隐藏@sco的写法
select s.*,
       case when @sco=s_sco then ''
            when @sco:=s_sco then @rank:=@rank+1 end as rn
from (select SId,
             sum(score) as s_sco
      from SC
      group by SId
      order by s_sco desc) as s,
     (select @rank:=0,@sco:=null) as t

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

-- 保留@sco的写法
select s.*,
       @rank:=if(@sco=s_sco,@rank,@rank+1) as rn,
       @sco:=s_sco
from (select SId,
             sum(score) as s_sco
      from SC
      group by SId
      order by s_sco desc) as s,
     (select @rank:=0,@sco:=null) as t

-- 隐藏@sco的写法
select s.*,
       case when @sco=s_sco then @rank
            when @sco:=s_sco then @rank:=@rank+1 end as rn
from (select SId,
             sum(score) as s_sco
      from SC
      group by SId
      order by s_sco desc) as s,
     (select @rank:=0,@sco:=null) as t

-- 窗口函数方法一
select *,rank() over(order by s_sco desc) as 'rank'
from (select SId,
             sum(score) as s_sco
      from SC
      group by SId) a
            
-- 窗口函数方法二
select SId,
       sum(score) as s_sco,
       rank() over(order by sum(score) desc) as 'rank'
from SC
group by SId

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 c.Cname,s.*
from (select CId,
             concat(sum(case when score<=60 and score>=0 then 1 else 0 end)/count(1)*100,'%') as '[0-60]',
             concat(sum(case when score<=70 and score>60 then 1 else 0 end)/count(1)*100,'%') as '[60-70]',
             concat(sum(case when score<=85 and score>70 then 1 else 0 end)/count(1)*100,'%') as '[70-85]',
             concat(sum(case when score<=100 and score>85 then 1 else 0 end)/count(1)*100,'%') as '[85-100]'
      from SC
      group by CId) as s
inner join Course as c on s.CId=c.CId

18.查询各科成绩前三名的记录

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

-- 窗口函数中的partition by用于定义分组排序的分组
select *
from
(select *,rank() over(partition by cid order by score desc) as rank_number
 from sc) as a
where rank_number in (1,2,3)
order by cid asc,score desc

19.查询每门课程被选修的学生数

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

21.查询男生、女生人数

select ssex,count(sid)
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

select a.sname,a.ssex,count(a.sname)
from student as a
join student as 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

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 cid,
       avg(score) as avg_sco
from sc
group by cid
order by avg_sco desc,cid 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,a.sname,b.avg_sco
from student as a
join (select sid,
             avg(score) as avg_sco
      from sc
      group by sid having avg_sco>=85) as b
on a.sid=b.sid

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 a.sname,b.score
from student as a
join (select sid,score
      from sc
      where score<60 and cid=(select cid
                              from course
                              where cname='数学')) as b
on a.sid=b.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 a.*,b.cid,b.score
from student as a
left join sc as 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 a.sname,b.cid,b.score
from student as a
right join sc as b on a.sid=b.sid
where b.score>70

30.查询不及格的课程

select distinct cid
from sc
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 sid,sname
from student
where sid in (select sid
              from sc
              where cid='01' and score>=80)

32.求每门课程的学生人数

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

33.假设成绩不重复，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 a.*,b.score
from student as a
join (select sid,score
      from sc
      where cid in (select cid
                    from course
                    where tid in (select tid
                                  from teacher
                                  where tname='张三'))) as b
on a.sid=b.sid
order by score desc
limit 1

34.假设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 *
from (select a.*,b.score,rank() over(order by b.score desc) as rank_number
      from student as a
      join (select sid,score
            from sc
            where cid in (select cid
                          from course
                          where tid in (select tid
                                        from teacher
                                        where tname='张三'))) as b
      on a.sid=b.sid) as a
where rank_number=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 distinct a.*
from sc as a
join sc as b
on a.sid=b.sid and a.score=b.score and a.cid!=b.cid

36.查询每门功成绩最好的前两名

select *
from (select *,row_number() over(partition by cid order by score desc) as row_num
      from sc) as a
where row_num in (1,2)

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(sid)
from sc
group by cid having count(sid)>5

38.检索至少选修两门课程的学生学号

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

39.查询选修了全部课程的学生信息

select sid,count(cid)
from sc
group by sid having count(cid)=(select count(cid)
                                from course)

40.查询各学生的年龄，只按年份来算

select *,year(now())-year(sage) as 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 *,timestampdiff(year,sage,now()) as age
from student

42.查询本周过生日的学生

select *
from student
where week(concat('2020-',substr(sage,6,5)))=week(now())

43.查询下周过生日的学生

select *
from student
where week(concat('2020-',substr(sage,6,5)))=week(now())+1

44.查询本月过生日的学生

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

45.查询下月过生日的学生

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