...
    $orderby = JRequest::getVar('orderby', 'registerDate');
    $direction = JRequest::getVar('direction', 'ASC');
    $search = JRequest::getVar('search', '');
    ...//ещё переменные & формирование 1го $query
    if ($search != "") {
        $query .= " WHERE (u.name LIKE '%$search%' OR u.username LIKE '%$search%')";
    }

    $kunena_db->setQuery($query);
    $total = $kunena_db->loadResult();
    ... //определение 2-го $query
    if ($search != "")
    {
        $query .= " WHERE (name LIKE '%$search%' OR username LIKE '%$search%')";
        $query_ext .= "&search=" . $search;
    }

    $query .= " ORDER BY $orderby $direction, id $direction";
    ... // +limit
    $kunena_db->setQuery($query);
...