查询每一门课的间接先行课的课程名称；
select first.cno,second.cpno,second.cname
from course first,course second
where first.cpno=second.cno;
查询所在系部为“MA”且选修了高等数学课程的学生姓名，年龄，性别；
select sname,sage,ssex
from student,course,sc
where student.sno=sc.sno and course.cno=sc.cno
and sdept='ma' and cname='数学'
查询选修了数据结构课程，且成绩在90分以上的学生学号；
select sno
from course,sc
where course.cno=sc.cno and cname='数据结构' and grade>90;
查询选修了数据结构课程，且成绩在90分以上的学生姓名，年龄；
select sname,sage
from course,sc,student
where student.sno=sc.sno and course.cno=sc.cno
and cname='数据结构' and grade>90;
查询选修了数据结构课程的学生学号，姓名，成绩；
select sc.sno,sname,grade
from course,sc,student
where student.sno=sc.sno and course.cno=sc.cno
and cname='数据结构';
查询所在系部为“MA”的女生人数；P98
select count(distinct sno)
from student
where sdept='ma' and ssex='女';
查询选修了2号课程的学生姓名；
select sname
from student,sc
where student.sno=sc.sno and cno='2';
查询没有选修2号课程的学生姓名；
select sname
from student
where not exists(
select sno
from sc
where student.sno=sc.sno and cno='2');
查询选修了全部课程的学生的姓名；P99
select sname
from student,sc
where student.sno=sc.sno
group by sname
having count(cno)>=7;
查询至少选修了学号为“201215121”的学生所选修的全部课程的学生学号和姓名；P111
select distinct sno
from sc scx
where not exists(
select *
from sc scy
where scy.sno='201215121' and
not exists
(select *
from sc scz
where scz.sno=scx.sno and scz.cno=scy.cno));
查询学生的总人数；（P97聚集函数）
select count(*)
from student;
查询每个系部的学生人数；
select count(sno) as number,sdept
from student
group by sdept;
查询选修了1号课程的学生人数；
select count(sno) as number
from sc
where cno='1';
查询选修了操作系统课程的学生人数；
select count(sc.sno) as number
from course,sc
where course.cno=sc.cno and cname='操作系统';
查询课程的课程号和选修该课程的人数；
select count(sc.sno) as number,cno
from sc
group by cno;
查询选修课超过3 门课的学生学号；
select sno
from sc
group by sno
having count(*)>3;
查询选修1号课程的最高分，平均分；
select max(grade) as max,avg(grade) as avg
from sc
where cno='1';
查询选修了数据库课程的最高分，平均分；
select max(grade) as max,avg(grade) as avg
from sc,course
where sc.cno=course.cno and cname='数据库';
查询系别为“CS“，选修2号课程的平均分；
select avg(grade) as avg
from sc,student
where sc.sno=student.sno and sdept='cs' and cno='2';
查询每个学生的学号，姓名，所修课程的平均分；
select sc.sno,sname,avg(grade)as avg
from student,sc
where student.sno=sc.sno
group by sc.sno,sname
查询指定学号的学生所获得的总学分。（成绩大于等于60，则获得该门课程的学分；学号自己给定）；
select student.sno,sname,sum(ccredit) as sum
from student,sc,course
where student.sno=sc.sno and course.cno=sc.cno
and grade>60 and sc.sno='201215121'
group by student.sno,student.sname
查询每个学生的学号，姓名，所获得的总学分（成绩大于等于60，则获得该门课程的学分）；
select student.sno,sname,sum(ccredit) as sum
from student,sc,course
where student.sno=sc.sno and course.cno=sc.cno and grade>60
group by student.sno,student.sname
查询每门课程的平均分，最高分
select avg(grade)as avg,max(grade) as max
from sc
group by cno;