public static function getSitesForUser($nb_user)
    {
        if (is_numeric ($nb_user_id = nb_getMixedValue($nb_user, NABU_USER_FIELD_ID))) {
            $retval = CNabuSiteUser::buildObjectListFromSQL(
                'nb_site_id',
                'SELECT su.*
                   FROM nb_site_user su, nb_user u, nb_site s
                  WHERE su.nb_user_id=u.nb_user_id
                    AND su.nb_site_id=s.nb_site_id
                    AND su.nb_user_id=%user_id$d',
                array(
                    'user_id' => $nb_user_id
                ),
                ($nb_user instanceof CNabuUser ? $nb_user : null)
            );
        } else {
            $retval = new CNabuSiteUserList();
        }

        return $retval;
    }