1. I assumed that you first connect to the database
2. then you need to have a "county" record in your "mydatase" table.
3. then its just a matter of setting the county to whatever you are trying to evaluate, assuming that is taken from the user you could use something like.
making 2 assumptions, 1 = your form method is "post" and your form = "county"
$county = trim(htmlspecialchars($_POST['county']));
....connect to database....
mysql_query("SELECT * FROM 'mydatabase' WHERE county='$county'")
or die("The ". mysql_error() . " error occured, and the query couldn't be performed");
if your form method is "get use $_GET and you can just rename the "county" inside if thats different as well
you should not trust user data directly from the user.