Tính tuổi

DECLARE @datestart DATE = '1996-11-12', @dateend DATE = GETDATE();
 
SELECT DATEDIFF(year, @datestart ,@dateend) + CASE WHEN (DATEADD(year,DATEDIFF(year, @datestart  ,@dateend) , @datestart) > @dateend) THEN - 1 ELSE 0 END AS age_year
 
SELECT DATEDIFF(year, @datestart ,@dateend) + IIF(DATEADD(year,DATEDIFF(year, @datestart  ,@dateend) , @datestart) > @dateend,-1, 0) AS age_year

1. GET DATE, FOMONTH, EOMONTH