-- 20150101这个学生 没有选修的课
SELECT cname
FROM course as c
WHERE 
	NOT EXISTS
(select * 
from score as sc
where c.cno = sc.cno 
and sno = 20150101);

-- 选了所有课的 学生姓名
SELECT sname
FROM student as s
WHERE 
NOT EXISTS
(
	SELECT cname
	FROM course as c
	WHERE 
		NOT EXISTS
		(select * 
		from score as sc
		where sc.cno = c.cno and sc.sno = s.sno
		)
)