Student(S#,Sname,Sage,Ssex) 学生表 Course(C#,Cname,T#) 课程表 SC(S#,C#,score) 成绩表 Teacher(T#,Tname) 教师表 问题： 1、查询“001”课程比“002”课程成绩高的所有学生的学号； select a.S# from (select s#,score from SC where C#=001) a,(select s#,score from SC where C#=002) b where a.scoreb.score and a.s#=b.s#; 2、查询平均成绩大于60分的同学的学号和平均成绩； select S#,avg(score) from sc group by S# having avg(score) 60; 3、查询所有同学的学号、姓名、选课数、总成绩； select Student.S#,Student.Sname,count(SC.C#),sum(score) from Student left Outer join SC on Student.S#=SC.S# group by Student.S#,Sname 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 Student.S#,Student.Sname from Student where S# not in (select distinct( SC.S#) from SC,Course,Teacher where SC.C#=Course.C# and Teacher.T#=Course.T# and Teacher.Tname=叶平); 6、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名； select Student.S#,Student.Sname from Student,SC where Student.S#=SC.S# and SC.C#=001and exists( Select * from SC as SC_2 where SC_2.S#=SC.S# and SC_2.C#=002); 7、查询学过“叶平”老师所教的所有课的同学的学号、姓名； select S#,Sname from Student where S# in (select S# from SC ,Course ,Teacher where SC.C#=Course.C# and Teacher.T#=Course.T# and Teacher.Tname=叶平 group by S# having count(SC.C#)=(select count(C#) from Course,Teacher where Teacher.T#=Course.T# and Tname=叶平); 8、查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名； Select S#,Sname from (select Student.S#,Student.Sname,score ,(select score from SC SC_2 where SC_2.S#=Student.S# and SC_2.C#=002) score2 from Student,SC where Student.S#=SC.S# and C#=001) S_2 where score2 60); 10、查询没有学全所有课的同学的学号、姓名； select Student.S#,Student.Sname from Student,SC where Student.S#=SC.S# group by Student.S#,Student.Sname having count(C#) =60 THEN 1 ELSE 0 END)/COUNT(*) AS 及格百分数 FROM SC T,Course where t.C#=course.C# GROUP BY t.C# ORDER BY 100 * SUM(CASE WHEN isnull(score,0)=60 THEN 1 ELSE 0 END)/COUNT(*) DESC 20、查询如下课程平均成绩和及格率的百分数(用1行显示): 企业管理（001），马克思（002），OO&UML （003），数据库（004） SELECT SUM(CASE WHEN C# =001 THEN score ELSE 0 END)/SUM(CASE C# WHEN 001 THEN 1 ELSE 0 END) AS 企业管理平均分 ,100 * SUM(CASE WHEN C# = 001 AND score = 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN C# = 001 THEN 1 ELSE 0 END) AS 企业管理及格百分数 ,SUM(CASE WHEN C# = 002 THEN score ELSE 0 END)/SUM(CASE C# WHEN 002 THEN 1 ELSE 0 END) AS 马克思平均分 ,100 * SUM(CASE WHEN C# = 002 AND score = 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN C# = 002 THEN 1 ELSE 0 END) AS 马克思及格百分数 ,SUM(CASE WHEN C# = 003 THEN score ELSE 0 END)/SUM(CASE C# WHEN 003 THEN 1 ELSE 0 END) AS UML平均分 ,100 * SUM(CASE WHEN C# = 003 AND score = 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN C# = 003 THEN 1 ELSE 0 END) AS UML及格百分数 ,SUM(CASE WHEN C# = 004 THEN score ELSE 0 END)/SUM(CASE C# WHEN 004 THEN 1 ELSE 0 END) AS 数据库平均分 ,100 * SUM(CASE WHEN C# = 004 AND score = 60 THEN 1 ELSE 0 END)/SU