public function andRespondentTracks($fields = '*', $groupBy = false) {
        $this->sql_select->join('gems__respondent2track',
                'gto_id_respondent_track = gr2t_id_respondent_track',
                $fields);

        if ($groupBy && is_array($fields)) {
            $this->sql_select->group($fields);
        }

        return $this;
    }