Ordering a query

I use the following code to order the results of the query by the variable $order. $result = mysql_query("SELECT articles.title,vote.votes,vote.total,articles.date,staff.firstname,articles.content,articles.id FROM staff,articles,vote WHERE articles.authorid = staff.id AND articles.id = vote.item ORDER BY $order DESC",$db); I assign the variable a value according to my url, http://www.mysite.com/file.php?order=something My question is. Is there a way of assigning the $order variable a default value? Like if they hit http://www.mysite.com/file.php without the order=something can I tell the script to assign $order a default value? Thanks, Nate