SQL User-defined Function for Calculating Age as of Today

Every now and then we need  an easy way to calculate age of something in a database application, e.g. employee age. Here I propose two SQL user-defined functions that can be used for the job. The first one is a table-valued function, and the second one is scalar-valued.

First function: FT_Age (table-valued)

CREATE FUNCTION [dbo].[FT_Age]
(
@IYEAR int,
@IMONTH int,
@IDAY int
)
RETURNS @AgeTable TABLE
(IYEAR int, IMONTH int, IDAY int)
WITH ENCRYPTION
AS
BEGIN

DECLARE @DDATE AS date,
@DLAST_MONTHLY AS date,
@ILAST_MONTH AS int,
@IMONTHLY_DAY AS int,
@DTODAY AS date,
@IYEARDIFF AS int,
@IMONTHDIFF AS int,
@IDAYDIFF AS int

SET @DTODAY = GETDATE()
SET @DDATE = DATEFROMPARTS(@IYEAR, @IMONTH, @IDAY)

SET @ILAST_MONTH = MONTH(DATEADD(MM, -1, @DTODAY))
SET @IMONTHLY_DAY = CASE WHEN @ILAST_MONTH = 2 AND DAY(@DDATE) > 28 THEN 28
WHEN @ILAST_MONTH IN (4,6,9,11) AND DAY(@DDATE) > 30 THEN 30
ELSE DAY(@DDATE) END
SET @DLAST_MONTHLY = DATEFROMPARTS(YEAR(@DTODAY), @ILAST_MONTH, @IMONTHLY_DAY)

SET @IYEARDIFF = DATEDIFF(YY, @DDATE, @DTODAY)
- CASE WHEN DATEADD(YY, DATEDIFF(YY, @DDATE, @DTODAY), @DDATE) > @DTODAY THEN 1 ELSE 0 END
SET @IMONTHDIFF = (DATEDIFF(MM, @DDATE, @DTODAY)
- CASE WHEN DATEADD(MM, DATEDIFF(MM, @DDATE, @DTODAY), @DDATE) > @DTODAY THEN 1 ELSE 0 END) % 12
SET @IDAYDIFF = DATEDIFF(DD, @DLAST_MONTHLY, @DTODAY)
INSERT INTO @AgeTable VALUES (@IYEARDIFF, @IMONTHDIFF, @IDAYDIFF)

RETURN
END

Usage example:
SELECT * FROM FT_Age(1945, 8, 17)

Second function: FN_Age (scalar-valued)

CREATE FUNCTION [dbo].[FN_Age]
(
@DDATE date,
@CDATE_PART char(2)
)
RETURNS INT
WITH ENCRYPTION
AS
BEGIN
DECLARE @DLAST_MONTHLY AS date,
@ILAST_MONTH AS int,
@IMONTHLY_DAY AS int,
@DTODAY AS date,
@IRETURN AS int

SET @DTODAY = GETDATE()

SET @ILAST_MONTH = MONTH(DATEADD(MM, -1, @DTODAY))
SET @IMONTHLY_DAY = CASE WHEN @ILAST_MONTH = 2 AND DAY(@DDATE) > 28 THEN 28
WHEN @ILAST_MONTH IN (4,6,9,11) AND DAY(@DDATE) > 30 THEN 30
ELSE DAY(@DDATE) END
SET @DLAST_MONTHLY = DATEFROMPARTS(YEAR(@DTODAY), @ILAST_MONTH, @IMONTHLY_DAY)

IF @CDATE_PART = 'YY' BEGIN
SET @IRETURN = DATEDIFF(YY, @DDATE, GETDATE()) - CASE WHEN DATEADD(YY, DATEDIFF(YY, @DDATE, GETDATE()), @DDATE) > GETDATE() THEN 1 ELSE 0 END
END
IF @CDATE_PART = 'MM' BEGIN
SET @IRETURN = (DATEDIFF(MM, @DDATE, GETDATE()) - CASE WHEN DATEADD(MM, DATEDIFF(MM, @DDATE, GETDATE()), @DDATE) > GETDATE() THEN 1 ELSE 0 END) % 12
END
IF @CDATE_PART = 'DD' BEGIN
SET @IRETURN = DATEDIFF(DD, @DLAST_MONTHLY, @DTODAY)
END


RETURN @IRETURN
END

Usage example:
SELECT RTRIM(CONVERT(CHAR(4), dbo.FN_Age(CONVERT(DATE, '19450817', 112), 'YY'))) + 'y '
+ RTRIM(CONVERT(CHAR(2), dbo.FN_Age(CONVERT(DATE, '19450817', 112), 'MM'))) + 'm '
+ RTRIM(CONVERT(CHAR(2), dbo.FN_Age(CONVERT(DATE, '19450817', 112), 'DD'))) + 'd ' AS Age

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