show user names that someones has referered to the site?

$referrers = DB_site->query("SELECT username,userid FROM user WHERE referrerid='X'");
echo("$bbuserinfo[username] has referred these users: ");
while ($referrer = mysql_fetch_array($referrers)) {
     ++$i
     echo("<a href=\"member.php?s=$session[sessionhash]&action=getinfo&userid=$referrers[userid]\">$referrers[username]</a>");
     if ($i < mysql_num_rows($referrers)) {
            echo(", ");
     }
}
echo(".");