PHP/MySQL User's Online Script

gistfile1.sql

CREATE TABLE `user_online` (
  `session` char(100) NOT NULL default '',
  `time` int(11) NOT NULL default '0'
) TYPE=MyISAM;

gistfile2.php

<?php
session_start();

$session     = session_id();
$time        = time();
$time_check  = $time-600;     //SET TIME 10 Minute

$host      = "localhost";     // Host name
$username  = "";              // Mysql username
$password  = "";              // Mysql password
$db_name   = "test";          // Database name
$tbl_name  = "user_online";   // Table name

// Connect to server and select databse
mysql_connect("$host", "$username", "$password")or die("cannot connect to server");
mysql_select_db("$db_name")or die("cannot select DB");

$sql     = "SELECT * FROM $tbl_name WHERE session='$session'";
$result  = mysql_query($sql);
$count   = mysql_num_rows($result);

if ($count == "0") {
  $sql1     = "INSERT INTO $tbl_name(session, time) VALUES('$session', '$time')";
  $result1  = mysql_query($sql1);
} else {
  $sql2     = "UPDATE $tbl_name SET time='$time' WHERE session = '$session'";
  $result2  = mysql_query($sql2);
}

$sql3               = "SELECT * FROM $tbl_name";
$result3            = mysql_query($sql3);
$count_user_online  = mysql_num_rows($result3);

echo "User online : $count_user_online";

// if over 10 minute, delete session 
$sql4     = "DELETE FROM $tbl_name WHERE time<$time_check";
$result4  = mysql_query($sql4);

// Open multiple browser page for result
// Close connection
mysql_close();