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How to calculate age in T-SQL with years, months, and days

On a project I was working on, I was required to calculate a persons age when they join the system; after looking on the internet I found various ways this could be done, but most of them had slight issues when it involved a Leap-Year.

The solution below is how I calculate number of years past / age. Hope this helps others

Answer 1

You need to add the following method to your database:

CREATE FUNCTION [dbo].[fnCalAge] (@DiffFrom DATE, @DiffTo DATE) RETURNS INT
AS
BEGIN
    DECLARE @NumOfYears INT
    SET @NumOfYears = (SELECT 
                         DATEDIFF(YEAR, @DiffFrom, @DiffTo) + 
                         CASE 
                           WHEN MONTH(@DiffTo) < MONTH(@DiffFrom) THEN -1 
                           WHEN MONTH(@DiffTo) > MONTH(@DiffFrom) THEN 0 
                           ELSE 
                             CASE WHEN DAY(@DiffTo) < DAY(@DiffFrom) THEN -1 ELSE 0 END 
                         END)
    IF @NumOfYears < 0
    BEGIN
        SET @NumOfYears = 0;
    END

    RETURN @NumOfYears;
END

You then call it in your SQL Query, similar to the following:

SET DATEFORMAT dmy 

SELECT dbo.fnCalAge(CAST('20/06/1987' AS DATE), CAST('20/06/2013' AS DATE))