Deference between start date and end date to display the another column

CREATE FUNCTION [dbo].FUN_GETMONTH(@date1 datetime, @date2 datetime)
RETURNS VARCHAR(1000)
AS
BEGIN

declare @tmp varchar(MAX)
 SET @tmp = ''
;with cte as (
select datename(month,@date1) as [Month_Name],@date1 as dat
union all 
select datename(month,DateAdd(Month,1,dat)),DateAdd(Month,1,dat) from cte 
where convert(char(6),DateAdd(Month,1,dat),112) <= convert(char(6),@date2,112)) 

select @tmp = @tmp +  CASE WHEN [Month_Name]='01' THEN 'JAN'
			 WHEN [Month_Name]='02' THEN 'FEB'
			  WHEN [Month_Name]='03' THEN 'MAR'
			   WHEN [Month_Name]='04' THEN 'APR'
			    WHEN [Month_Name]='05' THEN 'MAY'
			     WHEN [Month_Name]='06' THEN 'JUN'
			      WHEN [Month_Name]='07' THEN 'JUL'
			       WHEN [Month_Name]='08' THEN 'AUG'
			        WHEN [Month_Name]='09' THEN 'SEP'
			         WHEN [Month_Name]='10' THEN 'OCT'
			          WHEN [Month_Name]='11' THEN 'NOV'
			           WHEN [Month_Name]='12' THEN 'DEC' END + ', ' from CTE
			           option (maxrecursion 0)
			           RETURN @tmp;
 
END

DECLARE @TBL TABLE
(
    STRARTDATE DATETIME,
    ENDDATE    DATETIME
)
 
INSERT INTO @TBL(STRARTDATE, ENDDATE)
SELECT '2014-01-20', '2014-04-20'
UNION ALL
SELECT '2014-05-20', '2014-09-20'
UNION ALL
SELECT '2014-07-20', '2014-07-20'
UNION ALL
SELECT '2014-06-20', '2014-11-20'

select STRARTDATE,ENDDATE, dbo.FUN_GETMONTH(STRARTDATE, ENDDATE) AS MONTHS from @TBL