public function foldCase($key)
    {
        switch ($this->_caseFolding) {
            case Zend_Db::CASE_LOWER:
                $value = strtolower((string) $key);
                break;
            case Zend_Db::CASE_UPPER:
                $value = strtoupper((string) $key);
                break;
            case Zend_Db::CASE_NATURAL:
            default:
                $value = (string) $key;
        }
        return $value;
    }