This simple little function is normally called by other functions that calculate age, year differences.
When you run DATEPART DAYOFYEAR and compare the number of days on 3rd March then a leap year will be one more. To get around this, we append this function to one of the dates to add one day after February 29
CREATE FUNCTION Dates.GetLeapYear(@Date DATETIME2) RETURNS BIT AS BEGINDECLARE @Ret BIT=(CASE WHEN DATEPART(YEAR,@Date)%4<>0 OR (DATEPART(YEAR,@Date)%100=0 AND DATEPART(YEAR,@Date)%400<>0) THEN 0 ELSE 1 END)RETURN @RetENDGO
SELECT [dbo].[GetLeapYear]('01-01-1900') [1900],[dbo].[GetLeapYear]('01-01-1901') [1901],[dbo].[GetLeapYear]('01-01-1902') [1902],[dbo].[GetLeapYear]('01-01-1903') [1903],[dbo].[GetLeapYear]('01-01-1904') [1904]
Only 1904 will return true as expected.
