请教下面这句代码那里有有关问题?为什么总是提示ORDER附近有异常呢

请问下面这句代码那里有问题?为什么总是提示ORDER附近有错误呢?
set   rsp   =   server.CreateObject( "adodb.recordset ")  
            if   IsNumeric(categoryid)   then
                sql= "select   *   from   product   where   categoryid   =   "&categoryid& "   order   by   id   desc "
            else
                sql= "select   *   from   product   order   by   id   desc "
            end   if
        rsp.Open   sql,conn,1,1

------解决方案--------------------
1、判断categoryid是否有值
if categoryid= " " or isnull(categoryid）then categoryid=0

2、确认有ID这个字段
------解决方案--------------------
应该这样：
set rsp = server.CreateObject( "adodb.recordset ")
if categoryid <> " " then
if IsNumeric(categoryid) then
sql= "select * from product where categoryid = "&categoryid& " order by id desc "
else
sql= "select * from product order by id desc "
end if
end if
rsp.Open sql,conn,1,1