Controle PHP script - Online bezoekers

<?php
session_start();
if (isset($_GET['destroy'])){
	session_destroy ();
}
$ip=$_SERVER['REMOTE_ADDR'];
$time=time();
$timeout=120+$time; //is in seconden
$dbhost = ""; // MySQL host
$dbuser = ""; // MySQL gebruikersnaam
$dbpass = ""; // MySQL wachtwoord
$dbname = ""; // database naam



	$sql="INSERT INTO onlineusers (ip, timeout";

		if (isset($_SESSION['username'])){
			$sql .=", username";
		}

	$sql.=") VALUES ('".$_SERVER['REMOTE_ADDR']."', $timeout";
		if (isset($_SESSION['username'])){
			$sql .=", '".$_SESSION['username']."'";
		}
	$sql .=")";
	// Connect to MySQL Database
	mysql_connect($dbhost,$dbuser,$dbpass);
	mysql_select_db($dbname) or die("Geen database geselecteerd");
		if (!mysql_query($sql)){
		echo "Er mislukte iets...</br>Technische informatie: ".mysql_error()."</br>";
		}



$sql="DELETE FROM onlineusers WHERE timeout < ".$time;
	if (!mysql_query($sql)){
	echo "Er mislukte iets...</br>Techinische informatie: ".mysql_error();
	}

$uitslag=mysql_query("SELECT DISTINCT ip  FROM `onlineusers` WHERE `username` IS NULL") or echo "Ophalen van gegevens is mislukt (1)";
$aantal_ongeregistreert=mysql_num_rows($uitslag);
$uitslag2=mysql_query("SELECT DISTINCT ip   FROM `onlineusers` WHERE `username` IS NOT NULL") or echo "Ophalen van gegevens is mislukt (2)";;
$aantal_geregistreert=mysql_num_rows($uitslag2);


echo "Online bezoekers: ".$aantal_ongeregistreert;
echo "</br>";
echo "Online leden: ".$aantal_geregistreert;



//BEKIJK timeout en time
//echo "</br>";
//echo "Timeout: ".$timeout;
//echo "</br>";
//echo "Time---:    ".$time;
//echo "</br>";
//echo "time(); = ".time();
if ($time == $timeout){
	echo "Error! Time en timeout zijn gelijk";
}
//Bugger, zodat eventuele fouten kunnen worden weergeven
mysql_close();
?>