SELECT DATEDIFF(MONTH, '2009-04-16', '2009-05-15')

1

CREATE FUNCTION FullMonthsSeparation
(
    @DateA DATETIME,
    @DateB DATETIME
)
RETURNS INT
AS
BEGIN
    DECLARE @Result INT

    DECLARE @DateX DATETIME
    DECLARE @DateY DATETIME

    IF(@DateA < @DateB)
    BEGIN
    	SET @DateX = @DateA
    	SET @DateY = @DateB
    END
    ELSE
    BEGIN
    	SET @DateX = @DateB
    	SET @DateY = @DateA
    END

    SET @Result = (
    				SELECT
    				CASE
    					WHEN DATEPART(DAY, @DateX) > DATEPART(DAY, @DateY)
    					THEN DATEDIFF(MONTH, @DateX, @DateY) - 1
    					ELSE DATEDIFF(MONTH, @DateX, @DateY)
    				END
    				)

    RETURN @Result
END
GO

SELECT dbo.FullMonthsSeparation('2009-04-16', '2009-05-15') as MonthSep -- =0
SELECT dbo.FullMonthsSeparation('2009-04-16', '2009-05-16') as MonthSep -- =1
SELECT dbo.FullMonthsSeparation('2009-04-16', '2009-06-16') as MonthSep -- =2

SELECT DATEDIFF(DAY, '2009-04-16', '2009-05-15')/30
    , DATEDIFF(DAY, '2009-04-16', '2009-05-16')/30
    , DATEDIFF(DAY, '2009-04-16', '2009-06-16')/30

months_between(to_date ('2009/05/15', 'yyyy/mm/dd'),
               to_date ('2009/04/16', 'yyyy/mm/dd'))

round(months_between(to_date ('2009/05/15', 'yyyy/mm/dd'),
                     to_date ('2009/04/16', 'yyyy/mm/dd')))

select case when DATEPART(D,End_dATE) >=DATEPART(D,sTAR_dATE)
THEN ( case when DATEPART(M,End_dATE) = DATEPART(M,sTAR_dATE) AND DATEPART(YYYY,End_dATE) = DATEPART(YYYY,sTAR_dATE)
        THEN 0 ELSE DATEDIFF(M,sTAR_dATE,End_dATE)END )
ELSE DATEDIFF(M,sTAR_dATE,End_dATE)-1 END

SELECT 12 * (YEAR(end_date) - YEAR(start_date)) +
    ((MONTH(end_date) - MONTH(start_date))) +
    SIGN(DAY(end_date) / DAY(start_date));

Declare @Start DateTime
Declare @End DateTime

Set @Start = '11/1/07'
Set @End = '2/29/08'

Select DateDiff(Month, @Start, @End + 1)