经典50例

/*例1：查询“c1”课程比“c2”课程高的所有学生*/
select a.sno
from (select sno,score from sc where cno='c1') a,(select sno,score from sc where cno='c2') b
where a.sno=b.sno and a.score>b.score;
/*例2：查询平均成绩大于的同学的学号和平均成绩*/
select sno,avg(score)
from sc
group by sno
having avg(score)>60;
/*例3：查询所有同学的学号、姓名、选课数、总成绩*/
select student.sno,sname,count(cno),sum(score)
from student,sc
where student.sno=sc.sno
group by student.sno,sname;
/*例4：查询姓“李”的老师的个数*/
select count(distinct(tname))
from teacher
where tname like '李%';
/*例5：查询没学过“李玉”老师课的同学的学号和姓名*/
select sno,sname
from student
where sno not in
( select distinct(sc.sno)
from course,sc,teacher
where sc.cno=course.cno and course.tno=teacher.tno and tname='李玉'
);
/*例:6：查询学过“c1”并且也学过“c2”课程的的同学的学号和姓名*/
select student.sno,sname
from student,sc a,sc b
where student.sno=a.sno and student.sno=b.sno and a.cno='c1' and b.cno='c2';
/*另一种做法*/
select student.sno,sname
from student,sc
where student.sno=sc.sno and cno='c1' and exists
(select *
from sc a
where sc.sno=a.sno and a.cno='c2');
/*例7：查询学过“李玉”老师所教的所有课的同学的学号、姓名*/
select sno,sname
from student
where sno in
( select sno
from course,sc,teacher
where sc.cno=course.cno and course.tno=teacher.tno and teacher.tname='李玉'
group by sno
having count(course.cno)=(select count(cno)
from course,teacher
where course.tno=teacher.tno and tname='李玉' ));
/*例8：查询课程编号“c1”的成绩比课程编号“c2”课程低的所有同学的学号、姓名*/
select sno,sname
from (select student.sno,sname,score,(select score from sc a where a.sno=student.sno and a.cno='c2') score2
from student,sc
where student.sno=sc.sno and cno='c1') b
where score2>score;
/*另一种做法*/
select student.sno,sname
from student,sc a,sc b
where student.sno=a.sno and student.sno=b.sno and a.cno='c1' and b.cno='c2' and a.score<b.score;
/*例9：查询所有课程成绩小于60分的同学的学号、姓名*/
select sno,sname
from student
where sno not in
(select a.sno
from student a,sc
where a.sno=sc.sno and score>=60);
/*存在一个问题：没有选课的同学也会被筛选出来*/
/*例10：查询没有学全所有课的同学的姓名、学号*/
select student.sno,sname
from student,sc
where student.sno=sc.sno
group by student.sno,sname
having count(cno)<
(select count(cno) from course)
--存在问题：没有筛选出没有选课的同学#
/*例11：查询至少有一门课与学号为“1”的同学所学相同的同学的学号和姓名*/
select student.sno,sname
from student,sc
where student.sno=sc.sno and cno in (select cno from sc where sno='1') and student.sno!='1';
/*例12：查询至少学过学号为“1”同学所有一门课的其他同学的学号和姓名*/
select distinct(student.sno),sname
from student,sc
where student.sno=sc.sno and cno in (select cno from sc where sno='1') and student.sno!='1';
/*例13：把“sc”表中“李玉”老师教的课的成绩都改为此课程的平均成绩*/
--与在mysql中的区别
update SC
set score=(select avg(SC_2.score)from SC SC_2 where SC_2.Cno=SC.cno )
from Course,Teacher
where Course.cno=SC.cno and Course.tno=Teacher.tno and Teacher.Tname='李玉';
/*例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*/
select sc.sno,sname
from sc inner join student on student.sno=sc.sno
where cno in (select cno from sc where sno='2')
group by sc.sno,sname
having count(*)=(select count(*) from sc where sno='2')
/*例15：删除学习“叶平”老师课的sc表的记录*/
delete
from sc
where cno=(select cno
from course,teacher
where course.tno=teacher.tno and tname='李玉');
/*例16：向SC表中插入一些记录，符合以下：没有上过编号“”课程的同学学号,2号课的平均成绩*/
insert into sc(sno,cno,score)
select sno,'c2',(select avg(score) from sc where cno='c2')
from student
where sno not in (select sno from sc where cno='c2');
/*例17：按平均成绩从高到低显示所有学生的“管理学”、“经济学”、“R语言”三门的课程成绩，按如下形式显示：学生ID,管理学,经济学,R语言,有效课程数,平均分*/
select sno as 学生ID,
(select score from course,sc where t.sno=sc.sno and sc.cno=course.cno and cname='管理学') as 管理学,
(select score from course,sc where t.sno=sc.sno and sc.cno=course.cno and cname='经济学') as 经济学,
(select score from course,sc where t.sno=sc.sno and sc.cno=course.cno and cname='R语言') as R语言,
count(*) as 有效课程数,avg(t.score) as 平均成绩
from sc t
group by sno
order by avg(t.score);
/*例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*/
select cno as 课程ID,max(score) as 最高分,min(score) as 最低分
from sc
group by cno;
/*例19：按各科平均成绩从低到高和及格率的百分数从高到低顺序*/
select sc.cno,cname,avg(score) as 平均数,(100 * SUM(CASE WHEN isnull(score,0)>=60 THEN 1 ELSE 0 END)/COUNT(*)) as 及格百分数
from sc,course
where sc.cno=course.cno
group by sc.cno,cname
order by 平均数 ASC,及格百分数 DESC;
/*例20：查询如下课程平均成绩和及格率的百分数(用"1行"显示):管理学（c1），经济学（c2），R语言（c3））*/
select sum(case when cno='c1' then score else 0 end)/sum(case cno when 'c1' then 1 else 0 end) as 管理学平均分,
100 * SUM(CASE WHEN cno='c1' and isnull(score,0)>=60 THEN 1 ELSE 0 END)/sum(case when cno='c1' then 1 else 0 end) as 管理学及格百分数,
sum(case when cno='c2' then score else 0 end)/sum(case cno when 'c2' then 1 else 0 end) as 经济学平均分,
100 * SUM(CASE WHEN cno='c2' and isnull(score,0)>=60 THEN 1 ELSE 0 END)/sum(case when cno='c1' then 1 else 0 end) as 经济学学及格百分数,
sum(case when cno='c3' then score else 0 end)/sum(case cno when 'c3' then 1 else 0 end) as R语言平均分,
100 * SUM(CASE WHEN cno='c3' and isnull(score,0)>=60 THEN 1 ELSE 0 END)/sum(case when cno='c1' then 1 else 0 end) as R语言及格百分数
from sc;
/*例21：查询不同老师所教不同课程平均分从高到低显示*/
select tno,sc.cno,avg(score)
from sc,course
where sc.cno=course.cno
group by tno,sc.cno
order by avg(score) DESC;
/*例22：查询如下课程成绩第名到第6 名的学生成绩单：管理学（c1），经济学（c2），R语言（c3）
[学生ID],[学生姓名],管理学,经济学,R语言,平均成绩*/

--例23：统计列印各科成绩,各分数段人数:课程ID,课程名称,[100-85],[85-70],[70-60],[ <60]
select sc.cno as 课程ID,cname as 课程名称,
sum(case when score between 85 and 100 then 1 else 0 end)as [100-85],
sum(case when score between 70 and 85 then 1 else 0 end)as [85-70],
sum(case when score between 60 and 0100 then 1 else 0 end)as [70-60],
sum(case when score<60 then 1 else 0 end)as [<60]
from sc,course
where sc.cno=course.cno
group by sc.cno,cname;

--例24：查询学生平均成绩及其名次
SELECT 1+(SELECT COUNT( distinct 平均成绩)
FROM (SELECT sno,AVG(score) AS 平均成绩 FROM SC GROUP BY sno) AS T1
WHERE 平均成绩 > T2.平均成绩) as 名次, sno as 学生学号,平均成绩
FROM (SELECT sno,AVG(score) 平均成绩 FROM SC GROUP BY sno) AS T2
ORDER BY 平均成绩 desc;

--例25：查询各科成绩前三名的记录:(不考虑成绩并列情况)
select cno,sno,score
from sc
where score in(select top 3 score from sc x where x.cno=sc.cno order by score desc)
order by cno;

--例26：查询每门课程被选修的学生数
select cno,COUNT(*)as 人数
from sc
group by cno;
--例27：查询出只选修了一门课程的全部学生的学号和姓名
select sno,sname
from student
where sno in (
select sno
from sc
where sc.sno=student.sno
group by sno
having COUNT(*)=1);

--例28：查询男生、女生人数
select 男生人数,女生人数
from (select COUNT(*)as 女生人数 from student where ssex='女')as a,
(select COUNT(*)as 男生人数 from student where ssex='男') as b;

Select count(Ssex) as 男生人数 from Student group by Ssex having Ssex='男';
Select count(Ssex) as 女生人数 from Student group by Ssex having Ssex='女';
--例29：查询姓“张”的学生名单
select sname
from student
where sname like '张%';
--例30：查询同名同性学生名单，并统计同名人数
select sname,COUNT(*)
from student
group by sname
having COUNT(*)>1
--例31：年出生的学生名单(注：Student表中Sage列的类型是datetime)
--修改表的类型
alter table student
alter column  sage datetime;

select Sname, CONVERT(char (11),DATEPART(year,Sage)) as age
from student
where CONVERT(char(11),DATEPART(YYYY,Sage))='1981';
--例32:查询每门课程的平均成绩，结果按平均成绩升序排列，若相同，则按课程号降序排列
select cno,AVG(score)as 平均成绩
from sc
group by cno
order by AVG(score) asc,cno desc;
--例33:查询平均成绩大于的所有学生的学号、姓名和平均成绩
select sc.sno,sname,AVG(score)
from student,sc
where student.sno=sc.sno
group by sc.sno,sname
having AVG(score)>80;
--例34:查询课程名称为“管理学”，且分数低于的学生姓名和分数
select sname,isnull(score,0)
from student,sc,course
where student.sno=sc.sno and sc.cno=course.cno and cname='管理学' and score<60;
--例35:查询所有学生的选课情况
select sno,COUNT(*) as 选课数
from sc
group by sno;

SELECT SC.Sno,Sname,SC.cno,Cname
FROM SC,Student,Course
where SC.sno=Student.sno and SC.cno=Course.cno;
--例36:查询任何一门课程成绩在分以上的姓名、课程名称和分数
select distinct(sname),cname,score
from student,course,sc
where student.sno=sc.sno and sc.cno=course.cno and score>70;
--例37：查询不及格的课程，并按课程号从大到小排列
select distinct(cno)
from sc
where score<60
order by cno desc;
--例38:查询课程编号为c3且课程成绩在分以上的学生的学号和姓名
select student.sno,sname
from student,sc
where student.sno=sc.sno and cno='c3' and score>80;
--例39:求选了课程的学生人数
select count(distinct(sno))
from sc;
--例40：查询选修“叶平”老师所授课程的学生中，成绩最高的学生姓名及其成绩
select sname,MAX(score)
from sc,student
where sc.sno=student.sno and cno in
(select cno from teacher,course where teacher.tno=course.tno and tname='李玉')
group by sname;
--另一种做法
select Student.Sname,score
from Student,SC,Course C,Teacher
where sc.sno=student.sno and SC.cno=C.cno and C.tno=Teacher.tno and
Teacher.Tname='李玉' and SC.score=
(select max(score)from SC where Cno=C.cno);
--例41：查询各个课程及相应的选修人数
select cno,COUNT(*)
from sc
group by cno;
--例42:查询不同课程成绩相同的学生的学号、课程号、学生成绩
select distinct A.sno,B.score
from SC A ,SC B
where A.Score=B.Score and A.cno <>B.cno;
/*例43：查询每门功成绩最好的前两名*/
select sno as 学生ID,cno as 课程ID,score as 分数
from sc
where score in (select top 2 score from sc y where y.cno=sc.cno order by score desc) ;
/*例44：统计每门课程的学生选修人数。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 cno as 课程号,count(*) as 人数
from sc
group by cno
order by count(*) desc,cno asc;
/*例45：检索至少选修两门课程的学生学号*/
select sno
from sc
group by sno
having count(*)>=2;
/*例46：查询全部学生都选修的课程的课程号和课程名*/
/*同理：查询选修了全部课程的学生姓名*/
select cno,cname
from course
where  not exists
(select * from student
where not exists
(select * from sc
where sc.sno=student.sno and sc.cno=course.cno));
--下面一种方法更简单，全部课程都在学生选的课程中
select cno,cname
from course
where cno in (select cno from sc group by cno);
/*例47：查询没学过“李玉”老师讲授的任一门课程的学生姓名*/
select sname
from student
where sno not in( select sno
from sc,course,teacher
where sc.cno=course.cno and course.tno=teacher.tno and tname='李玉');
/*例48：查询两门以上不及格课程的同学的学号及平均成绩*/
select sno,avg(isnull(score,0))
from sc
where sno in(select sno
from sc
where score<60
group by sno
having count(*)>=2)
group by sno;
/*例49：检索“c2”课程分数小于*，按分数降序排列的同学学号*/
select sno
from sc
where cno='c2' and score<60
order by score DESC;
/*例50：删除“”同学的“c1”课程的成绩*/
delete
from sc
where sno='2'and cno='c1';