50条常用sql语句（以学生表为例）

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“”课程比“”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.score>b.score AND a.s#=b.s#; 
2、查询平均成绩大于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“”并且也学过编号“”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#='001'and 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“”的成绩比课程编号&ldqu