Bagaimana mendapatkan nilai dari URL

URL situs web:

http://www.example.com/?id=2

Kode:

$id = intval($_GET['id']);
$results = mysql_query("SELECT * FROM next WHERE id=$id");    
while ($row = mysql_fetch_array($results))     
{       
    $url = $row['url'];
    echo $url; //Outputs: 2
}