public function consume($dsql, $tick = true)
    {
        if ($dsql === UNDEFINED) {
            return '';
        }
        if ($dsql === null) {
            return '';
        }
        if (is_object($dsql) && $dsql instanceof Field) {
            $dsql = $dsql->getExpr();
        }
        if (!is_object($dsql) || !$dsql instanceof self) {
            return $tick ? $this->bt($dsql) : $dsql;
        }
        $dsql->params = &$this->params;
        $ret = $dsql->_render();
        if ($dsql->mode === 'select') {
            $ret = '('.$ret.')';
        }
        unset($dsql->params);
        $dsql->params = array();

        return $ret;
    }