/*Student(Sno,Sname,Sage,Ssex) 学生表
Course(Cno,Cname,Tno) 课程表
SC(Sno,Cno,score) 成绩表
Teacher(Tno,Tname) 教师表 */
1、查询“3”课程比“4”课程成绩高的所有学生的学号；
select a.sno
from (select sno,score from sc where cno=‘3‘ )a,
(select sno,score from sc where cno=‘4‘)b
where a.score>b.score and a.sno=b.sno;
2、查询平均成绩大于60分的同学的学号和平均成绩；
select sno,avg(score)
from sc
group by sno having avg(score)>60;
/*select sno,avg(score)
from sc where score>60 group by sno;这个为啥不行呢？*/
3、查询所有同学的学号、姓名、选课数、总成绩；
select a.sno,a.sname,count(b.cno),sum(c.score)
from student a,
course b,
sc c
where a.sno=c.sno and c.cno=b.cno
group by a.sno;
4、查询姓“李”的老师的个数；
select count(distinct(tname)) from teacher where tname like ‘%李%‘;
5、查询没学过“叶平”老师课的同学的学号、姓名；
select a.sno,a.sname
from student a
where a.sno not in(select distinct(b.sno) from sc b,course c,teacher d
where b.cno=c.cno and c.tno=d.tno and d.tname=‘叶平‘);
6、查询学过“3”并且也学过编号“4”课程的同学的学号、姓名；
select a.sno,a.sname
from student a,sc b
where a.sno=b.sno and b.cno=‘3‘ and exists(select * from sc as sc_01 where sc_01.sno=b.sno and sc_01.cno=‘4‘);
7、查询学过“叶平”老师所教的所有课的同学的学号、姓名；
select a.sno,a.sname
from student a
where a.sno in(select distinct(b.sno) from sc b,course c,teacher d
where b.cno=c.cno and c.tno=d.tno and d.tname=‘叶平‘ group by sno having count(b.cno)=
(select count(cno) from course c,teacher d where d.tno=c.tno and d.tname=‘叶平‘));
8、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 b where a.sno=b.sno and b.score>‘60‘);
9、查询没有学全所有课的同学的学号、姓名；
select a.sname,a.sno
from student a,sc b
where a.sno=b.sno
group by a.sno,a.sname
having count(cno)<(select count(*) from course);
10、查询至少有一门课与学号为“5”的同学所学相同的同学的学号和姓名；
select a.sno,a.sname
from student a,sc b
where a.sno=b.sno and b.cno in(select b.cno from sc b where b.sno=‘5‘);

11、删除学习“叶平”老师课的SC表记录；
delete sc
from sc,course,teacher
where course.cno=sc.cno and course.tno=teacher.tno and teacher.tname=‘叶平‘;

12、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 h.score as ‘最高分‘,l.score as ‘最低分‘,h.cno as ‘课程ID‘
from sc h,sc l
where h.cno=l.cno
and h.score=(
select max(IL.score) from sc IL,student IM where IL.cno=h.cno and IM.sno=IL.sno group by IL.cno)
and l.score=(
select min(IR.score) from sc IR where IR.cno=l.cno group by IR.cno);
13、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) 平均成绩
FROM SC
GROUP BY Sno ) T1
WHERE 平均成绩 > T2.平均成绩) 名次, Sno 学生学号,平均成绩
FROM (SELECT sno,AVG(score) 平均成绩 FROM SC GROUP BY sno ) T2
ORDER BY 平均成绩 desc;
14、查询各科成绩前三名的记录:(不考虑成绩并列情况)
SELECT t1.Sno as 学生ID,t1.Cno as 课程ID,t1.Score as 分数
FROM SC t1
WHERE score IN (SELECT TOP 3 score
FROM SC
WHERE t1.Cno= Cno
ORDER BY score DESC)
ORDER BY t1.Cno;
15、查询每门功成绩最好的前两名
SELECT t1.Sno as 学生ID,t1.Cno as 课程ID,Score as 分数
FROM SC t1
WHERE score IN (SELECT TOP 2 score
FROM SC
WHERE t1.Cno= Cno
ORDER BY score DESC )
ORDER BY t1.Cno;

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