private function _queryPDO($sql, array $params = array())
    {
        try {
            $this->_queryId = self::$_linkId->prepare($sql);
            $i = 1;
            foreach ($params as $key => $val) {
                $type = $this->getPDOConstantType($val);
                $this->_queryId->bindValue($i, $val, $type);
                ++$i;
            }
            return $this->_queryId->execute();
        } catch (PDOException $e) {
            $this->_error = $e->getMessage();
            return false;
        }
    }