I am still learning SQL so this may seem a very odd question, but is this the best way to use CASE within a CASE to check for NULL?
@FN_InputDt datetime)
RETURNS varchar(3)
as
BEGIN
DECLARE @Result varchar(3),
@MonthNo int
Set @MonthNo = datepart(m,@FN_InputDt)
Set @Result =
CASE WHEN @FN_InputDt IS NOT NULL then
CASE @MonthNo
WHEN 1 then 'JAN'
WHEN 2 then 'FEB'
WHEN 3 then 'MAR'
WHEN 4 then 'APR'
WHEN 5 then 'MAY'
WHEN 6 then 'JUN'
WHEN 7 then 'JUL'
WHEN 8 then 'AUG'
WHEN 9 then 'SEP'
WHEN 10 then 'OCT'
WHEN 11 then 'NOV'
WHEN 12 then 'DEC'
END
END
RETURN @Result
END