protected function _getFieldList()
    {
        $fields[] = $this->_getFieldsFor($this->_sql);

        foreach ($this->_sql->getJoins() as $join) {
            $str = $this->_getFieldsFor($join);
            if (!$str) {
                continue;
            }
            $fields[] = $str;
        }
        return implode(', ', $fields);
    }