Display online users

[Jamie_Garland]

this code shows the top 5 users

how do i get it to show the users that are currently online?

<?php
$connect = mysql_connect("","","") or die("Couldn't connect!");
mysql_select_db("prkscouk_users") or die("Couldn't find database");

$query = mysql_query("SELECT * FROM users ORDER BY id DESC LIMIT 5");

$numrows = mysql_num_rows($query);

if ($numrows > 0){
      while ($row = mysql_fetch_assoc($query))
    {
        $id = $row['id'];
        $username = $row['username'];
$email = $row['email'];
        echo "<a href=mailto:$email>$username</a><br>";
    }
}
else
{
     echo "No users were found.";
}
?>