Scalar Function with CTE Fails

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