You changed your url mid-stream, originally it was ?domain= now it is ?action=. That is the variable name in $_GET[''].
So, if you want to see if the variable is found in the database, one way is:
PHP Code:
<?
connect to and select database
$compare = $_GET['action'];
$sql = "select domain from table where domain='".$compare."'"; // field names equal to your database setup
if (mysql_query($sql)) {
echo "it is there in the database.";
} else {
echo "that domain is not in the database.";
}
?>