select sn from s where
not exists(select * from (select cno from s,sc
where s.sno=sc.sno and sn='赵亦') x where
not exists(select * from sc where s.sno=sc.sno
and )) and sn<>'赵亦'
select sn from s where
not exists(select * from (select cno from s,sc
where s.sno=sc.sno and sn='赵亦') x where
not exists(select * from sc where s.sno=sc.sno
and )) and sn<>'赵亦'