Scalar Function with CTE Fails - sql

Question

This function return is a single float value, but it always is null. Why?
Function to calculate the total working hour per employee:
ALTER FUNCTION GetTotalWorkingHour
(
#StartDate datetime,
#EndDate datetime,
#EmpID nvarchar(6) = null
)
RETURNS float
AS
BEGIN
DECLARE #Result float;
WITH
CTE_Start
AS
(
SELECT EmpID ,SUM(DATEDIFF(minute, (CAST(att.[date] AS datetime) + att.[Time]), #StartDate) *
CASE WHEN Funckey = 'EMPIN' THEN +1 ELSE -1 END) AS SumStart
FROM PERS_Attendance AS att
WHERE (EmpID = #EmpID OR #EmpID IS NULL) AND att.[date] < #StartDate GROUP BY EmpID
)
,CTE_End
AS
(
SELECT EmpID ,SUM(DATEDIFF(minute, (CAST(att.[date] AS datetime) + att.[Time]), #EndDate) * CASE WHEN Funckey = 'EMPIN' THEN +1 ELSE -1 END) AS SumEnd
FROM PERS_Attendance AS att
WHERE (EmpID = #EmpID OR #EmpID IS NULL) AND att.[date] < #EndDate GROUP BY EmpID
)
SELECT #Result =
(CTE_Start.SumStart - ISNULL(CTE_End.SumEND, 0) / 60.0) --AS SumHours
FROM
CTE_End
LEFT JOIN CTE_Start ON CTE_Start.EmpID = CTE_End.EmpID
RETURN #Result
END
GO
the above code run in a correct way and give me the expected result if i use it in a single query(not in function), so what's wrong?

Answer 1

i found the solution, it was a small bug, i must add:
SELECT #Result =
(SumEnd - ISNULL(SumStart, 0)) / 60.0 --AS SumHours
FROM
CTE_End
LEFT JOIN CTE_Start ON CTE_Start.EmpID = CTE_End.EmpID
RETURN #Result
instead of:
SELECT #Result =
(CTE_Start.SumStart - ISNULL(CTE_End.SumEND, 0) / 60.0) --AS SumHours
FROM
CTE_End
LEFT JOIN CTE_Start ON CTE_Start.EmpID = CTE_End.EmpID
RETURN #Result