ALTER FUNCTION [dbo].[GetYearlyDays] (Scalar-valued Functions (Can return any types of value like int or varchar etc))

 ALTER FUNCTION [dbo].[GetYearlyDays] 

(

@stDate date,

@endDate date,

@year int

)

RETURNS int

AS

BEGIN 

    DECLARE @noOfdays int

SELECT  @noOfdays=count(year(CurrentDate)) 

FROM (SELECT TOP (DATEDIFF(DAY, @stDate, @endDate) + 1)

CurrentDate = DATEADD(DAY, ROW_NUMBER() OVER(ORDER BY A.object_id) - 1, @stDate) 

FROM sys.all_objects A) AS B 

Where year(CurrentDate)=2020

group by year(CurrentDate)

RETURN @noOfdays

END

Call : select [dbo].[GetYearlyDays] ('01-01-2021','01-12-2021',2021)