16查询所有学生的sname，cname和degree列
--sname -->student
--cname -->course
--degree--score
select sname,cname ,degree from student,course,score
where student.sno=score.sno and course.cno=score.cno;
select sname,cname ,degree ,student.sno as stu_sno ,course.cno as cou_cnofrom student,course,score
where student.sno=score.sno and course.cno=score.cno;
17查询95031班学生每门课的平均分
先将95031班所有学生的信息找出来 select * from student where class =\'95031\';
select sno * from student where class =\'95031\';
select * from score where sno in (select sno * from student where class =\'95031\' );
select cno ,avg(degree)
from score
where sno
in (select sno * from student where class =\'95031\' )
group by cno;
18、查询选修3-105课程的成绩高于109号同学3-105成绩的所有同学的记录。（所有选修3-105课程的同学中，哪些是高于109号同学的成绩）
select degree from score where sno=\'109\' and cno=\'3-105\';
select *from score where cno=\'3-105\' and degree>(select degree from score where sno=\'109\' and cno=\'3-105\')
19查询成绩高于学号为109，课程号为3-105同学的成绩的同学的所有记录
select * from score where degree >（select degree from score where sno =\'109\' and cno=\'3-105\'）;