查询每门课程最高分的学生的学号，课程号，成绩

select t1.sid,t1.cid,t1.score
from score t1
where t1.score =
(
select max(t2.score)
from score t2
where t2.cid = t1.cid
group by t2.cid
)

select t1.sid,s.name,t1.cid,t1.score
from score t1
inner join stu s
on t1.sid=s.id
where t1.score =
(
select max(t2.score)
from score t2
where t2.cid = t1.cid
group by t2.cid
)