access能不能用百分比来剔除商品

seedwu

SELECT a.*
FROM [ALL] AS a
WHERE (select count(1) from [ALL] as b where a.grp_no=b.grp_no and b.amnt>=a.amnt) <=80
ORDER BY a.section_no, a.grp_no, a.subgrp_no, a.amnt DESC;

如语句,能做到的只能按照amnt的数值,来选出a.grp_no的前80个商品

所以问下能不能达到: 选出按照amnt的数值选出a.grp_no的前80%的商品,谢谢