protected function _getSqlSelectFieldsForTree($sTable, $aColumns = null)
    {
        if ($aColumns && count($aColumns)) {
            foreach ($aColumns as $key => $val) {
                $aColumns[$key] .= ' as ' . $val;
            }

            return "$sTable." . implode(", $sTable.", $aColumns);
        }

        $sFieldList = "$sTable.oxid as oxid, $sTable.oxactive as oxactive,"
                      . " $sTable.oxhidden as oxhidden, $sTable.oxparentid as oxparentid,"
                      . " $sTable.oxdefsort as oxdefsort, $sTable.oxdefsortmode as oxdefsortmode,"
                      . " $sTable.oxleft as oxleft, $sTable.oxright as oxright,"
                      . " $sTable.oxrootid as oxrootid, $sTable.oxsort as oxsort,"
                      . " $sTable.oxtitle as oxtitle, $sTable.oxdesc as oxdesc,"
                      . " $sTable.oxpricefrom as oxpricefrom, $sTable.oxpriceto as oxpriceto,"
                      . " $sTable.oxicon as oxicon, $sTable.oxextlink as oxextlink,"
                      . " $sTable.oxthumb as oxthumb, $sTable.oxpromoicon as oxpromoicon";

        $sFieldList .= $this->getActivityFieldsSql($sTable);

        return $sFieldList;
    }