SQL using #table/ Temp table inside a table valued function - sql

Question

I need to have a function to get all the week numbers in a given date range.
I have to seperate this from my stored procedure since it has a lengthy process.
But when I use #tables in side the function it gives following error
Msg 2772, Level 16, State 1, Procedure WeekNumbersWithinRange, Line 19
Cannot access temporary tables from within a function.
And here is my function.
CREATE FUNCTION WeekNumbersWithinRange
(
#FromDate DATETIME,
#ToDate DATETIME
)
RETURNS TABLE
AS
BEGIN
IF OBJECT_ID (N'tempdb..#WeeksofRange', N'U') IS NOT NULL
BEGIN
DROP TABLE #WeeksofRange
END
CREATE TABLE #WeeksofRange (WeekNo INT);
-- Get all week numbers for the given delivery date range
IF OBJECT_ID (N'tempdb..#Calendar', N'U') IS NOT NULL
BEGIN
DROP TABLE #Calendar
END
CREATE TABLE #Calendar
(
CalendarDate DATE PRIMARY KEY,
IsWeekend BIT,
YearNo SMALLINT,
QuarterNo TINYINT,
MonthNo TINYINT,
DayOfYearNo SMALLINT,
DayNo TINYINT,
WeekNo TINYINT,
WeekDayNo TINYINT
)
DECLARE #beginDate DATE, #endDate DATE
SELECT
#beginDate = #FromDate, #endDate = #ToDate
WHILE #beginDate <= #endDate
BEGIN
INSERT INTO #Calendar (CalendarDate, IsWeekend, YearNo, QuarterNo, MonthNo, DayOfYearNo, DayNo, WeekNo, WeekDayNo)
SELECT
#beginDate As CalendarDate,
(CASE WHEN DATEPART(Weekday, #beginDate) IN (7, 1)
THEN 1 ELSE 0
END) AS IsWeekend,
DATEPART(Year, #beginDate) AS YearNo,
DATEPART(QUARTER, #beginDate) AS QuarterNo,
DATEPART(MONTH, #beginDate) AS MonthNo,
DATEPART(DayOfYear, #beginDate) AS DayOfYearNo,
DATEPART(Day, #beginDate) AS DayNo,
DATEPART(Week, #beginDate) AS WeekNo,
DATEPART(WEEKDAY, #beginDate) AS WeekDayNo
--,(Case When #beginDate < '02/03/2011' Then 0 Else DATEPART(Week, #beginDate) - 5 End) As mySpecificWeekNo
SET #beginDate = DATEADD(Day, 1, #beginDate)
END
INSERT INTO #WeeksofRange
SELECT DISTINCT WeekNo
FROM #Calendar;
-- End of Select all week numbers in the range
SELECT * FROM #WeeksofRange
GO
Is there any other way to do this? Or do I need to write this logic inside my stored procedure?

Answer 1

You cannot use a Temp table in UDF because
the object can't be created inside UDF.
Instead of using a Temp table, use a table variable, that should solve your problem
CREATE FUNCTION WeekNumbersWithinRange
(
#FromDate DATETIME,
#ToDate DATETIME
)
RETURNS TABLE
AS
BEGIN
DECLARE #WeeksofRange TABLE
(
WeekNo INT
)
-- Get all week numbers for the given delivery date range
declare #Calendar table
(CalendarDate Date Primary key, IsWeekend Bit, YearNo SmallInt, QuarterNo TinyInt, MonthNo TinyInt, DayOfYearNo SmallInt, DayNo TinyInt, WeekNo TinyInt, WeekDayNo TinyInt )
Declare #beginDate Date, #endDate Date
Select #beginDate = #FromDate , #endDate = #ToDate
While #beginDate <= #endDate
Begin
Insert Into #Calendar (CalendarDate, IsWeekend, YearNo, QuarterNo, MonthNo, DayOfYearNo, DayNo, WeekNo, WeekDayNo)
Select
#beginDate As CalendarDate
,(Case When DATEPART(Weekday, #beginDate) In (7, 1) Then 1 Else 0 End) As IsWeekend
,DATEPART(Year, #beginDate) As YearNo
,DATEPART(QUARTER, #beginDate) As QuarterNo
,DATEPART(MONTH, #beginDate) As MonthNo
,DATEPART(DayOfYear, #beginDate) As DayOfYearNo
,DATEPART(Day, #beginDate) As DayNo
,DATEPART(Week, #beginDate) As WeekNo
,DATEPART(WEEKDAY, #beginDate) As WeekDayNo
--,(Case When #beginDate < '02/03/2011' Then 0 Else DATEPART(Week, #beginDate) - 5 End) As mySpecificWeekNo
Set #beginDate = DateAdd(Day, 1, #beginDate)
End
INSERT INTO #calendar
SELECT DISTINCT WeekNo FROM #Calendar;
-- End of Select all week numbers in the range
SELECT * FROM #WeeksofRange
GO

Answer 2

I'd normally choose to make the Calendar table permanent and populate it with, say, a centuries worth of rows. And then just query it.
But, if you have to have this function, you can write it to use a CTE and avoid any explicit state/iteration management:
CREATE FUNCTION WeekNumbersWithinRange
(
#FromDate DATETIME,
#ToDate DATETIME
)
RETURNS TABLE
AS
return (With Weeks as (
select DATEPART(week,#FromDate) as Week,#FromDate as dt
union all
select DATEPART(week,ndt),ndt
from Weeks
cross apply (select DATEADD(day,7,dt) as ndt) t
where
ndt < #ToDate
)
select Week from Weeks
union
select DATEPART(week,#ToDate)
)
I've made the simplifying assumption that week numbers only change every 7 days so we don't need to generate a row for every day inside the CTE. Also, I use the final UNION to make sure that the final week is included. It could be skipped since I'm working in 7 day increments, so we could jump our value straight from a previous week to a value greater than #ToDate.
Depending on the ranges you're working with, you may have to apply the MAXRECURSION option to the query to allow the CTE to work fully.