sql 查询没有选秀c1，也没有选修c2的学生学号、课程号和成绩该怎么写？

SELECT sno,cno,score
from sc
where (cno<>'C1') AND (CNO<>'C2')

这样并不对诶

SELECT sno,cno,score
from sc
where cno No in ('C1','C2')

SELECT sno,cno,score FROM sc WHERE (cno<>'C1') AND (CNO<>'C2') AND sno NOT IN(SELECT sno FROM sc WHERE cno in('C1','C2'));