private static function merge($sql, $binds) {
	if (is_array($binds) == false) {
		$binds = (array)$binds;
	}
	if (is_null(self::$connection)) {
		$exception = bootstrap::get_library('exception');
		$response  = bootstrap::get_library('response');
		throw new $exception('no db connection', $response::STATUS_SERVICE_UNAVAILABLE);
	}
	
	foreach ($binds as &$argument) {
		$argument = self::$connection->real_escape_string($argument);
	}
	
	return vsprintf($sql, $binds);
}