一道SQL语句的面试题目

今天一个朋友发了一道题目给我，我把此题目贴出来，以便大伙看看，共同研究研究。

题目：

已知关系模式：

1、s (sno,sname) 学生关系。sno 为学号，sname 为姓名
2、c (cno,cname,cteacher) 课程关系cno 为课程号，cname 为课程名，cteacher 为任课教师
3、sc(sno,cno,scgrade) 选课关系。scgrade 为成绩
要求实现如下5 个处理：
1．找出没有选修过“李明”老师讲授课程的所有学生姓名
2．列出有二门以上（含两门）不及格课程的学生姓名及其平均成绩
3．列出既学过“1”号课程，又学过“2”号课程的所有学生姓名
4．列出“1”号课成绩比“2”号同学该门课成绩高的所有学生的学号
5．列出“1”号课成绩比“2”号课成绩高的所有学生的学号及其“1”号课和“2”号课的成绩

解题：

1．找出没有选修过“李明”老师讲授课程的所有学生姓名

Select Sname As 学生姓名 From s Where Not Exists (Select * From c, Sc Where c.Cno = Sc.Cno And Cteacher = '李明' And Sc.Sno = s.Sno);Select Sname As 学生姓名 From s Where Sno Not In (Select Sno From c, Sc Where c.Cno = Sc.Cno And Cteacher = '李明');

2. 列出有二门以上(含两门)不及格课程的学生姓名及其平均成绩

Select s.Sno As 学生学号, s.Sname As 学生姓名, Avg(Sc.Scgrade) As 平均成绩 From s, Sc Where Sc.Sno = s.Sno And Sc.Sno In (Select Sc.Sno From Sc Where Sc.Scgrade < 60 Group By Sc.Sno Having Count(*) > 2) Group By s.Sno, s.Sname;

3. 列出既学过“01”号课程，又学过“02”号课程的所有学生姓名

select s.sno as 学生学号,s.sname as 学生姓名 from s where sno in(select sc.sno as 学生学号 from c,sc where c.cno=sc.cno and c.cno in('01','02') group by sno having count(distinct sc.cno)=2);

4. 列出“01”号课成绩比“02”号同学该门课成绩高的所有学生的学号

select sc1.sno as 学生学号 from sc as sc1,c as c1,sc as sc2,c as c2where sc1.cno=c1.cno and c1.cno='01' and sc2.cno=c2.cno and c2.cno='02'and sc1.scgrade>sc2.scgrade group by sc1.sno;

5. 列出“01”号课成绩比“02”号课成绩高的所有学生的学号及其“01”号课和“02”号课的成绩

select sc1.sno as 学生学号, sc1.scgrade as no1grade ,sc2.scgrade as no2gradefrom sc as sc1,c as c1,sc as sc2,c as c2where sc1.cno=c1.cno and c1.cno='01' and sc2.cno=c2.cno and c2.cno='02'and sc1.scgrade>sc2.scgrade group by sc1.sno;