stu（id,name）
cla-stu（stuid,claid）
sco（stuid,score）
select claid from cla-stu where =
and stuid in (
select stuid from sco where score>)
group by claid having count(stu)>
stu（id,name）
cla-stu（stuid,claid）
sco（stuid,score）
select claid from cla-stu where =
and stuid in (
select stuid from sco where score>)
group by claid having count(stu)>
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