protected function _buildQueryElementConcatId()
{
$str = parent::_buildQueryElementConcatId();
$jointable = $this->getJoinModel()->getJoin()->table_join;
$dbtable = $this->actualTableName();
$db = JFactory::getDbo();
$table =& $this->getListModel()->getTable();
$fullElName = $this->getFullName(false, true, false) . "_id";
$str .= ", (SELECT GROUP_CONCAT(" . $this->_element->name . " SEPARATOR '" . GROUPSPLITTER . "') FROM {$jointable} WHERE parent_id = " . $table->db_primary_key . ") AS {$fullElName}";
return $str;
}