急请日期相减有关问题请问!

急请日期相减问题请教!!!!!
SQL= "select   *   from   publicfile   where   datediff( 'd ',date1,now())> =byday "  

其中:   date1     是SQL   server中的datetime   类型.

byday   是int   整型   (天数)  


那么以上执行为何不行呢?   请指教,谢谢.


------解决方案--------------------
SQL= "select * from publicfile where datediff( 'd ',date1,now())> = " & byday
------解决方案--------------------

datediff(day,date1,getdate())
------解决方案--------------------
SQL= "select * from publicfile where datediff(d,date1,now())> = "&byday
------解决方案--------------------
datediff(d,date1,now()) 把 'd '改成 d 即可.
------解决方案--------------------
SQL= "select * from publicfile where datediff( 'd ',date1,getdate()) > = " & byday