楼主你好,
select s.sname,c.cname,t.grade
from (select * from (select * from sc order by sid,grade desc)t group by sid) t
inner join s on s.sid = t.sid
inner join c on c.cid = t.cid
select s.sname,c.cname,t.grade
from (select * from (select * from sc order by sid,grade desc)t group by sid) t
inner join s on s.sid = t.sid
inner join c on c.cid = t.cid
select a. Sname,b. Cname,d.Grade
from Sid a, C b,(
select id,
from SC c
where not exists (select 1 from SC where Grade<Grade))d
where a.id=d. Sid and b. Cid=d.Cid