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
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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;
9、查询所有课程成绩小于60分的同学的学号、姓名;
select S#,Sname from Student where S# not in (select Student.S# from Student,SC where s.S#=SC.S# and score>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#) <(select count(C#) from Course);
11、查询至少有一门课与学号为“1001”的同学所学相同的同学的学号和姓名;
select S#,Sname from Student,SC where Student.S#=SC.S# and C# in select C# from SC where S#=’1001’;

12、查询至少学过学号为“001”同学所有一门课的其他同学学号和姓名;
select distinct SC.S#,Sname from Student,SC
where Student.S#=SC.S# and C# in (select C# from SC where S#=’001’);
13、把“SC”表中“叶平”老师教的课的成绩都更改为此课程的平均成绩;
update SC set score=(select avg(SC_2.score) from SC SC_2
where SC_2.C#=SC.C# ) from Course,Teacher where Course.C#=SC.C# and Course.T#=Teacher.T# and Teacher.Tname=’叶平’);
14、查询和“1002”号的同学学习的课程完全相同的其他同学学号和姓名;
select S# from SC where C# in (select C# from SC where S#=’1002’)
group by S# having count()=(select count() from SC where S#=’1002’);
15、删除学习“叶平”老师课的SC表记录;
delect SC from Course ,Teacher
where Course.C#=SC.C# and Course.T#= Teacher.T# and Tname=’叶平’;
16、向SC表中插入一些记录，这些记录要求符合以下条件：没有上过编号“003”课程的同学学号、2、
号课的平均成绩;
insert SC select S#,’002’,(select avg(score)
from SC where C#=’002’) from Student where S# not in (select S# from SC where C#=’002’);