อยากได้ code user online ครับ ทำไงดีครับ เขียนเองไม่เป็นครับ

<?php
$Session_name = "default";
$host = "localhost"; // Server
$username = ""; // User Mysql
$password = ""; // Password Mysql
$database = "mydatabase"; // ชื่อฐานข้อมูล
$table = "useronline"; // ชื่อ Table



if ($Session_name == "default") {
session_start();
}
else {
session_name("$Session_name");
session_start("$Session_name");
}

$SID = session_id();
$time = time();
$dag = date("z");
$nu = time()-900; // Keep for 15 mins


mysql_connect ($host, $username, $password) OR DIE ("Could not connect to MySQL");
mysql_select_db($database) OR DIE ("Can't select database.");


$sidcheck = mysql_query("SELECT count(*) FROM $table WHERE SID='$SID'");
$sid_check = mysql_result($sidcheck,0);

if ($sid_check == "0") {

mysql_query("INSERT INTO $table VALUES ('$SID','$time','$dag')");
} else {

mysql_query("UPDATE $table SET time='$time' WHERE SID='$SID'");
}


$count_users = mysql_query("SELECT count(*) FROM $table WHERE time>$nu AND day=$dag");
$users_online = mysql_result($count_users,0);
echo $users_online; // echo จำนวนผู้ online ออกมาก


mysql_query("DELETE FROM $table WHERE time<$nu");
mysql_query("DELETE FROM $table WHERE day != $dag");

mysql_close();

?>