ALTER FUNCTION get_partition_string(@datetime datetime = null )
  RETURNS character varying(14) AS
BEGIN
	DECLARE @partition_string varchar(14);
	IF (@datetime is NULL)
	BEGIN
		SET @datetime = getdate();
	END
	set @partition_string = (select lower(datename(month, @datetime) + '_' + datename(year, @datetime)));
	RETURN @partition_string;
END;

--select dbo.get_partition_string(default);