mySQL 50个查询系列

http://bubufx.com/detail-1749088.html

http://www.jb51.net/article/67932.htm

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.score>b.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#='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“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 <score;