public static function set_db($db, $connection_name = self::DEFAULT_CONNECTION)
        {
            self::_setupDbConfig($connection_name);
            self::$_db[$connection_name] = $db;

            if(!is_null(self::$_db[$connection_name])) {
                self::_setupIdentifierQuoteCharacter($connection_name);
                self::_setupLimitClauseStyle($connection_name);
            }
        }