MySQL数据库 - 50道SQL强化练习题 - 参考答案 - 零度的脚步

MySQL数据库 - 50道SQL强化练习题 - 参考答案

mysql数据库SQL强化练习

参考答案如下：（仅供参考）

select A.*,B.C#,B.score from (select * from SC where C#=\'01\')A
left join(select * from SC where C#=\'02\')B
on A.S#=B.S#
where A.score>B.score
--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 * from (select * from SC where C#=\'01\')A
left join (select * from SC where C#=\'02\')B on A.S#=B.S#
where B.S# is not null
--1.1 查询同时存在" 01 "课程和" 02 "课程的情况
 
select * from (select * from SC where C#=\'01\')A
left join (select * from SC where C#=\'02\')B on A.S#=B.S#
--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 * from SC where C#=\'02\'and S# not in(select S# from SC where C#=\'01\')
--1.3 查询不存在" 01 "课程但存在" 02 "课程的情况
 
select A.S#,B.Sname,A.dc from(select S#,AVG(score)dc from SC group by S#)A
left join Student B on A.S#=B.S# where A.dc>=60
--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 * from Student where S# in (select distinct S# from SC)
--3. 查询在 SC 表存在成绩的学生信息
 
select B.S#,B.Sname,A.选课总数,A.总成绩 from
(select S#,COUNT(C#)选课总数,sum(score)总成绩 from SC group by S#)A
right join Student B on A.S#=B.S#
--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.S#,B.Sname,A.选课总数,A.总成绩 from
(select S#,COUNT(C#)选课总数,sum(score)总成绩 from SC group by S#)A
left join Student B on A.S#=B.S#
--4.1 查有成绩的学生信息
 
select COUNT(*)李姓老师数量 from Teacher where Tname like \'李%\'
--5.查询「李」姓老师的数量
 
select * from Student
where S# in(select distinct S# from SC
where C#=(select C# from Course
where T#=(select T# from Teacher where Tname=\'张三\')))
--6.查询学过「张三」老师授课的同学的信息
 
select * from Student where S# in(select S# from SC group by S# having COUNT(C#)<3)
--7.查询没有学全所有课程的同学的信息
 
select * from Student
where S# in(select distinct S# from SC where C# in(select C# from SC where S#=\'01\')
)
--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
where S# in(select S# from SC where C# in(select distinct C# from SC where S#=\'01\') and S#<>\'01\'
group by S#
having COUNT(C#)>=3)
--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 Sname from Student
where S# not in(select S# from SC
where C# in(select C# from Course where T# in(select T# from Teacher where Tname=\'张三\')
)
)--10. 查询没学过「张三」老师讲授的任一门课程的学生姓名
 
select A.S#,A.Sname,B.平均成绩 from Student A right join
(select S#,AVG(score)平均成绩 from SC where score<60 group by S# having COUNT(score)>=2)B
on A.S#=B.S#--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 S#,score from SC where C#=\'01\' and score<60 order by score desc
--12.检索" 01 "课程分数小于 60 ，按分数降序排列的学生信息
 
select S#,max(case C# when \'01\' then score else 0 end)\'01\',
max(case C# when \'02\' then score else 0 end)\'02\',
MAX(case C# when \'03\' then score else 0 end)\'03\',AVG(score)平均分 from SC
group by S# order by 平均分 desc
--13. （静态写法）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 distinct A.C#,Cname,最高分,最低分,平均分,及格率,中等率,优良率,优秀率 from SC A
left join Course on A.C#=Course.C#
left join (select C#,MAX(score)最高分,MIN(score)最低分,AVG(score)平均分 from SC group by C#)B on A.C#=B.C#
left join (select C#,(convert(decimal(5,2),(sum(case when score>=60 then 1 else 0 end)*1.00)/COUNT(*))*100)及格率 from SC group by C#)C on A.C#=C.C#
left join (select C#,(convert(decimal(5,2),(sum(case when score >=70 and score<80 then 1 else 0 end)*1.00)/COUNT(*))*100)中等率 from SC group by C#)D on A.C#=D.C#
left join (select C#,(convert(decimal(5,2),(sum(case when score >=80 and score<90 then 1 else 0 end)*1.00)/COUNT(*))*100)优良率 from SC group by C#)E on A.C#=E.C#
left join (select C#,(convert(decimal(5,2),(sum(case when score >=90 then 1 else 0 end)*1.00)/COUNT(*))*100)优秀率
from SC group by C#)F on A.C#=F.C#
--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
 
select *,RANK()over(order by score desc)排名 from SC
--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 *,DENSE_RANK()over(order by score desc)排名 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
 
select *,RANK()over(order by 总成绩 desc)排名 from(
select S#,SUM(score)总成绩 from SC group by S#)A
--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
 
select *,dense_rank()over(order by 总成绩 desc)排名 from(
select S#,SUM(score)总成绩 from SC group by S#)A
--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 distinct A.C#,B.Cname,C.[100-85],C.所占百分比,D.[85-70],D.所占百分比,E.[70-60],E.所占百分比,F.[60-0],F.所占百分比
from SC A
left join Course B ON A.C#=B.C#
left join (select C#,sum(case when score>85 and score<=100 then 1 else null end)[100-85],
convert(decimal(5,2),(sum(case when score>85 and score<100 then 1 else null end))*1.00/COUNT(*))*100 所占百分比 from SC group by C#)C on A.C#=C.C#
left join (select C#,sum(case when score>70 and score<=85 then 1 else null end)[85-70],
convert(decimal(5,2),(sum(case when score>70 and score<=85 then 1 else null end))*1.00/COUNT(*))*100 所占百分比 from SC group by C#)D on A.C#=D.C#
left join (select C#,sum(case when score>60 and score<=70 then 1 else null end)[70-60],
convert(decimal(5,2),(sum(case when score>60 and score<=70 then 1 else null end))*1.00/COUNT(*))*100 所占百分比 from SC group by C#)E on A.C#=E.C#
left join (select C#,sum(case when score>0 and score<=60 then 1 else null end)[60-0],
convert(decimal(5,2),(sum(case when score>0 and score<=60 then 1 else null end))*1.00/COUNT(*))*100 所占百分比 from SC group by C#)F on A.C#=F.C#
--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 * from(select *,rank()over (partition by C# order by score desc)A from SC)B where B.A<=3
--18. 查询各科成绩前三名的记录（方法 1）
 
select a.S#,a.C#,a.score from SC a
left join SC b on a.C#=b.C# and a.score<b.score
group by a.S#,a.C#,a.score
having COUNT(b.S#)<3
order by a.C#,a.score desc
--18. 查询各科成绩前三名的记录（取 a 的最高分与本表比较）（方法 2）
 
select * from SC a where (select COUNT(*)from SC where C#=a.C# and score>a.score)<3
order by a.C#,a.score desc
--18. 查询各科成绩前三名的记录（取 a）(方法 3)
 
select C#,COUNT(S#)学生数 from SC group by C#
--19. 查询每门课程被选修的学生数
 
select S#,Sname from Student
where S# in(select S# from(select S#,COUNT(C#)课程数 from SC group by S#)A where A.课程数=2)
--20. 查询出只选修两门课程的学生学号和姓名
 
select Ssex,COUNT(Ssex)人数 from Student group by Ssex
--21. 查询男生、女生人数
 
select * from Student where Sname like \'%风%\'
--22. 查询名字中含有「风」字的学生信息
 
select A.*,B.同名人数 from Student A
left join (select Sname,Ssex,COUNT(*)同名人数 from Student group by Sname,Ssex)B
on A.Sname=B.Sname and A.Ssex=B.Ssex
where B.同名人数>1
--23. 查询同名同性学生名单，并统计同名人数
 
select * from Student where YEAR(Sage)=1990
--24.查询 1990 年出生的学生名单
 
select C#,AVG(score)平均成绩 from SC group by C# order by 平均成绩 desc,C#
--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 A.S#,A.Sname,B.平均成绩 from Student A
left join (select S#,AVG(score)平均成绩 from SC group by S#)B on A.S#=B.S#
where B.平均成绩>85
--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 B.Sname,A.score from(select * from SC where score<60 and C#=(select C# from Course where Cname=\'数学\'))A
left join Student B on A.S#=B.S#
-- 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.S#,B.C#,B.score from Student A left join SC B on A.S#=B.S#
-- 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.Sname,D.Cname,D.score from
(select B.*,C.Cname from(select * from SC where score>70)B left join Course C on B.C#=C.C#)D
left join Student A on D.S#=A.S#
-- 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 * from SC where score<60
-- 30. 查询不及格的课程
 
select A.S#,B.Sname from (select * from SC where score>80 and C#=01)A
left join Student B on A.S#=B.S#
--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 C#,COUNT(*)学生人数 from SC group by C#
--32. 求每门课程的学生人数
 
select top 1* from SC
where C#=(select C# from Course where T#=(select T# from Teacher where Tname=\'张三\'))
order by score desc
--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 *from(select *,DENSE_RANK()over (order by score desc)A
from SC
where C#=(select C# from Course where T#=(select T# from Teacher where Tname=\'张三\')))B
where B.A=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 C.S#,max(C.C#)C#,max(C.score)score from SC C
left join(select S#,avg(score)A from SC group by S#)B
on C.S#=B.S#
where C.score=B.A
group by C.S#
having COUNT(0)=(select COUNT(0)from SC where S#=C.S#)
--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 * from
(select *,ROW_NUMBER()over(partition by C# order by score desc)A from SC)B
where B.A<3
--36. 查询每门功成绩最好的前两名
 
select C#,COUNT(S#)选修人数 from SC
group by C#
having COUNT(S#)>5
order by 选修人数 desc,C#
--37.统计每门课程的学生选修人数（超过5人的课程才统计）。
--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
 
select S# from SC
group by S#
having COUNT(C#)>=2
--38. 检索至少选修两门课程的学生学号
 
select S# from SC
group by S#
having count(C#)=(select distinct COUNT(0)a from Course)
--39. 查询选修了全部课程的学生信息
 
select S#,datediff(yy,Sage,GETDATE())年龄 from Student
--40. 查询各学生的年龄，只按年份来算
 
select *,(case when convert(int,\'1\'+substring(CONVERT(varchar(10),Sage,112),5,8))
<convert(int,\'1\'+substring(CONVERT(varchar(10),GETDATE(),112/*112是将格式转化为yymmdd*/),5,8))
then datediff(yy,Sage,GETDATE())
else datediff(yy,Sage,GETDATE())-1
end)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
--方法是把时间转化成 Int 格式来做条件比较大小，判断是否超期，
 
select *,(case when datename(wk,convert(datetime,(convert(varchar(10),year(GETDATE()))+substring(convert(varchar(10),Sage,112),5,8))))=DATENAME(WK,GETDATE())
then 1 else 0 end)生日提醒
from Student
--42. 查询本周过生日的学生
--方法：采取将生日转化为当年日期，再转化为本年中的第几个星期进行判断搜出结果
 
select *,(case when datename(wk,convert(datetime,(convert(varchar(10),year(GETDATE()))+
substring(convert(varchar(10),Sage,112),5,8))))=DATENAME(WK,GETDATE())+1
then 1 else 0 end)生日提醒
from Student
--43. 查询下周过生日的学生
 
select *,(case when month(convert(datetime,(convert(varchar(10),year(GETDATE()))+substring(convert(varchar(10),Sage,112),5,8))))=month(GETDATE())
then 1 else 0 end)生日提醒
from Student
--44. 查询本月过生日的学生
 
select *,(case when month(convert(datetime,(convert(varchar(10),year(GETDATE()))+substring(convert(varchar(10),Sage,112),5,8))))=month(GETDATE())+1
then 1 else 0 end)生日提醒
from Student
--45. 查询下月过生日的学生