这两条sql语句，高手竟然都。。。

SELECT student.sno,student.sname FROM student where sno !=(
SELECT sno FROM sc WHERE cno=(select cno from course where tno=(select tno FROM teacher where tname='叶平')));

select student.sno,student.sname from student
where sno not in (select distinct(sc.sno) from sc,course,teacher
where sc.cno=course.cno and teacher.tno=course.tno and teacher.tname='叶平')
请问 这两条sql 语句有什么效率上的优劣吗？？？

效率都不高 为什么不考虑用exists呢 这个效率比你写的两个都高