$user_ip=$_SERVER['REMOTE_ADDR'];
$user_agent=$_SERVER['HTTP_USER_AGENT'];
$entry_time=time();
$exit_time=time()+(10*60);

if(!empty($user_agent))
{
        if(empty($_SESSION['id']))
        {
        $re= mysql_query("SELECT user_ip FROM guests WHERE user_ip = '".$user_ip."'");

            if(mysql_num_rows($re) == 0)
            {
            mysql_query("INSERT INTO guests (user_ip, entry_time, exit_time, user_agent) VALUES ('".$user_ip."','".$entry_time."','".$exit_time."','".$user_agent."')");
            }

        $total = mysql_num_rows(mysql_query("SELECT * FROM guests"));

        mysql_query("DELETE * FROM guests WHERE exit_time= '".$entry_time."'");
        }
}