1
select sdept fom student group by sdept having count(*)>=200
2
select a.cname 课程,b.cname 先修课
from course a left join course b on a.cpno=b.cno
3
select a.sno,a.sname,a.sgender,a.sage,a.sdept,b.cno,isnull(b.grade,0)
from student a left join sc b on a.sno=b.sno
4
update sc set grade=0 where sno in (select sno from student where sdept='CS')
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