select sno from sc where cno in ( select cno from sc where sno in( select sno from sc where cno='s003'))
哦,那个S003是SNO(学号),不是课程号
select sno from sc where cno in (select cno from c inere join sc on c.cno=sc.cno where c.sno='s003')
select distinct x.sno, x.sname from t_s as x, t_sc as y where ( (select count(*) from t_sc as z where z.sno = x.sno ) >= (select count(*) from t_sc where t_sc.sno = 's003') and x.sno <> 's003' )
where c.sno='s003')
where
(
(select count(*) from t_sc as z where z.sno = x.sno ) >=
(select count(*) from t_sc where t_sc.sno = 's003') and x.sno <> 's003'
)