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)S
SId 学生编号,CId 课程编号,score 分数
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 SC a
left join Student d
on a.Sid=d.Sid
inner join SC b
on a.SID=b.Sid and a.Cid='01' and b.Cid='02'
where a.score>b.score;
1.1 查询同时存在" 01 "课程和" 02 "课程的情况
select *
from SC a
inner join SC b
on a.Sid=b.Sid and a.Cid='01' and b.Cid='02'
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 (select * from SC where Cid='01') a
left join SC b
on a.Sid=b.Sid and b.Cid='02';
写法2：
select *
from SC a
left join SC b
on a.Sid=b.Sid and b.Cid='02'
where a.Cid='01';
1.3 查询不存在"01 "课程但存在" 02 "课程的情况
select *
from SC a
inner join SC b
on a.Sid=b.Sid and b.Cid='02'
where a.Sid not in(select Sid from SC where Cid='01');
写法2：
select *
from SC
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,a.Sname,b.avg_score
from Student a
inner join
(select Sid,avg(score) as avg_score
from SC
group by Sid having avg(score)>=60) b
on a.Sid=b.Sid;
3.查询在 SC 表存在成绩的学生信息
select a.*
from Student a
inner join
(select distinct Sid from SC) b
on a.Sid=b.Sid;
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,b.count_c,b.sum_score
from Student a
left join
(select Sid,count(Cid) as count_c,sum(score) as sum_score
from SC
group by Sid ) b
on a.Sid=b.Sid;
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')));
写法2：
select Student.*
from Student,SC,Course,Teacher
where Teacher.Tname='张三'
and Teacher.Tid=Course.Tid
and Course.Cid=SC.Cid
and SC.Sid=Student.Sid;
7.查询没有学全所有课程的同学的信息
select a.*,cons
from Student a
inner join
(select Sid,count(Cid) as cons
from SC
group by Sid having cons<(select count(Cid) from Course))b
on a.Sid=b.Sid;
写法2：
select a.*,cons
from Student a,
(select Sid,count(Cid) as cons
from SC
group by Sid having cons<(select count(Cid) from Course))b
where a.Sid=b.Sid;
算上未学过课程的同学的情况：
select *
from Student
where Sid not in
(select Sid
from SC
group by Sid having count(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 b.*
from (select distinct Sid
from SC
where Cid in(select Cid from SC where Sid='01')) a,
Student b
where a.Sid=b.Sid;
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 SC a
inner join Student b
on a.Sid=b.Sid
where a.Sid not in(select Sid from SC where Cid not in(select Cid from SC where Sid='01'))
and a.Sid!='01'
group by a.Sid
having count(*)=(select count(*) 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.*,avg(Score)
from Student a
inner join SC b
on a.Sid=b.Sid
where b.score<60
group by a.Sid
having count(*)>=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 a.*,Score
from Student a
right join
(select Sid, Score from SC where Cid='01' and Score<60) b
on a.Sid=b.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 Sid,avg(Score) as avg_score 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
select Cid,max(Score) as 最高分,min(Score) as 最低分,avg(Score) as 平均分,
sum(case when sc.score>=60 then 1 else 0 end)/count(*) as 及格率,
sum(case when sc.score>=70 and score<80 then 1 else 0 end)/count(*) as 中等率,
sum(case when sc.score>=80 and score<90 then 1 else 0 end)/count(*) as 优良率,
sum(case when sc.score>=90 then 1 else 0 end)/count(*) as 优秀率,
count(*) as 选修人数
from SC group by Cid
order by 选修人数 desc,Cid asc;
15.按各科成绩进行排序，并显示排名， Score重复时继续排名
select Sid,Cid,Score,@rank:=@rank+1 as rn
from SC,(select @rank:=0)t
order by Score desc;
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,
case when @sco=Score then@rank
else @rank:=@rank+1 end as rn,
@sco:=Score
from SC,(select @rank:=0,@sco:=null)t
order by Score desc;
写法2：（可以去掉上面写法中多出来的@sco:=Score这一列）
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
select a.*,@rank:=if(@sco=scos,'',@rank+1) as rn,
@sco:=scos
from(select sid,sum(Score) as scos
from SC
group by Sid
order by scos desc)a,
(select @sco:=null,@rank:=0)b;
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:=if(@sco=scos,@rank,@rank+1) as rn,
@sco:=scos
from(select sid,sum(Score) as 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,Course.Cname,
concat(sum(case when score>=85 and score<=100 then 1 else 0 end)/count(*)*100,'%') as '[85-100]',
concat(sum(case when score>=70 and score<85 then 1 else 0 end)/count(*)*100,'%') as '[70-85)',
concat(sum(case when score>=60 and score<70 then 1 else 0 end)/count(*)*100,'%') as '[60-70)',
concat(sum(case when score>=0 and score<60 then 1 else 0 end)/count(*)*100,'%') as '[0-60)'
from SC
inner join Course
on SC.Cid=Course.Cid
group by SC.Cid;
18.查询各科成绩前三名的记录
不考虑Score重复的情况：
select a.*
from SC a
where (select count(*) from SC b
where b.Cid=a.Cid and b.Score>a.Score)<3
order by Cid asc,score desc;
Score 重复时合并名次的情况：
select Sid,Cid,Score,rn from
(select SC.*,@rank:=if(@ci=Cid,if(@sco=Score,@rank,@rank+1),1) as rn,
@sco:=Score,@ci:=Cid
from SC,(select @rank:=0,@sco:=null,@ci:=null)b
order by Cid asc,Score desc)a
where rn<=3;
19.查询每门课程被选修的学生数
select Cid,count(*) as cons from SC
group by Cid
order by Cid asc
20.查询出只选修两门课程的学生学号和姓名
select a.Sid,Sname
from Student a,SC b
where a.Sid=b.Sid
group by Sid
having count(*)=2;
21.查询男生、女生人数
select Ssex,count(*) as cons
from Student
group by Ssex;
22.查询名字中含有「风」字的学生信息
select Student.* 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.*,cons
from Student a
left join (select Sname,Ssex,count(*) as cons from Student group by Sname,Ssex)b
on a.Sname=b.Sname and a.Ssex=b.Ssex
where cons>1;
24.查询 1990 年出生的学生名单
select Student.* 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)
from SC
group by Cid
order by Score 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,Sname,avg_score
from Student a
right join (select Sid,avg(Score) as avg_score
from SC
group by Sid
having avg_score>=85) 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 Sname,Score
from Student a,SC b
where a.Sid=b.Sid and Score<60
and b.Cid =(select Cid from Course where Cname='数学');
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 * from Student a left join SC 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 Student a,SC b,Course c
where a.Sid=b.Sid and b.Cid=c.Cid and 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(*) 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.*,max(Score)
from Student a,SC b,Course c,Teacher d
where a.Sid=b.Sid and b.Cid=c.Cid and c.Tid=d.Tid and Tname='张三';
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 e.*,
case when @sco=Score then @rank
when @sco:=Score then @rank:=@rank+1 end as rn
from (select a.*,Score
from Student a,SC b,Course c,Teacher d
where a.Sid=b.Sid and b.Cid=c.Cid and c.Tid=d.Tid and Tname="张三"
order by Score desc)e,(select @rank:=0,@sco:=null)f)g
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 * from
SC a
where a.Sid in(select Sid from SC b
where a.Sid=b.Sid and a.Cid!=b.Cid and a.Score=b.Score);
36.查询每门功成绩最好的前两名
select * from
(select a.*,
@rank:=if(@ci=Cid,if(@sco=Score,@rank,@rank+1),1) as rn,
@sco:=Score,@ci:=Cid
from (select SC.* from SC order by Cid asc,Score desc)a,
(select @rank:=0,@sco:=null)b)c
where rn<=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(*) from SC group by Cid having count(*)>5;
38.检索至少选修两门课程的学生学号
select Sid,count(*) from SC group by Sid having count(*)>=2;
39.查询选修了全部课程的学生信息
select a.* from Student a
where Sid in(select Sid from SC
group by Sid having count(*)=(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 *,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;