Newbie question on wildcards

Please could somebody help with this little problem. I use the following query

$query = "select ID,make,model,type,engine,year,yearletter,colour,doors,status,price,city,county from cars where (make = '$make' and model = '$model' and county = '$county' and price <= '$price')";

Now this works fine but some people have said that it would be better if there was a option to search using "any county" Could I add an option to the county drop down menu in my search form saying "Any" and then use a wildcard ? in the value section.

I believe if they select "any", you could just remove the "and country='$country'" clause. In effect you would be not selecting on a country, therefore any country matches.