-- Description:	Возраст человека с днем рождения @Birthday на дату @Date. Если @Date is null, то возраст вычисляется на текущий момент.
/*
  select * from [dbo].[Age]('20170101', '20160101')
*/
ALTER FUNCTION [dbo].[Age] 
(	
	@Birthday datetime, 
	@Date datetime = null
)
RETURNS TABLE 
AS
RETURN 
( with dt0 as ( select [@Date] = isnull( @Date, getdate() ) )
     , dt as ( select [@Date], YearDiff = datediff( year, @Birthday, dt0.[@Date] ) from dt0 )
	select  Age = YearDiff
                  + ( sign( datediff(day, @Birthday, dateadd(year, -dt.YearDiff, dt.[@Date] ) ) ) - 1 ) / 2
	  from dt
)