H21107-随堂练习1

例14 查询选修了课程名为“信息系统”的学生学号和姓名.

select Sno,Sname

from Student

where Sno in (

    select Sno from SC where Cno IN (

         select Cno from Course where Cname='信息系统'

         )

    );

例17 查询考试平均成绩高于全体学生的总平均成绩的学生学号和平均成绩

select Sno,avg(Grade)as '平均成绩'

from SC

group by Sno

having avg(Grade)>(select avg(Grade) from SC)

例21 查询所有学习了1号课程的学号和姓名

select Sno,Sname

from Student

where Sno in(select Sno from SC where Cno='1')