Load Different Code Depending On Number Of URL Variables

Currently, when I'm building dynamic pages I build a page (for example, default.asp?ID=2) to process one variable within the dynamic URL (ID), and find myself having to create a seperate page if I want to process 2 variables for the same content (i.e default.asp?ID=2&Dt=3).

Surely there's a way of loading different content on the page depending if the URL you to the page has either one or more URL variables - is there a way of doing this? I've been thinking about it, and would it be simplest just writing an IF statement (e.g : if the URL contains only one URL variable, load this content, if it contains 2 URL variables, load this other content.

Would someone please be able to give me an example of how this IF statement would be written?, as I've never had the need to write an IF statement before. If you are able to give me an example of the IF statement I'm after, would you be kind enough to comment it aswell so I can understand the methodology behind it?