protected function setClause($section, $clause)
    {
        if(!isset($this->selectParams[$section]))
            $this->selectParams[$section] = array();

        if(empty($clause))
            unset($this->selectParams[$section]);
        else if(is_array($clause))
            $this->selectParams[$section] = array_merge($this->selectParams[$section], $clause);
        else
            $this->selectParams[$section][] = $clause;

    }