public function setGroup()
    {
        // set group position if exist

        $group = [];

        foreach ($this->data['group'] as $table => $params) {

            $params = array_flip($params);

            if (empty($params) === false) {

                foreach ($params as $field) {
                    $group[] = $table . '.' . $field;
                }
            }
        }
        $this->builder->groupBy($group);

        return null;
    }