SQL Group and Sum By Month - Default to Zero

Question

I am currently grouping and summing inventory usage by month:

SELECT      Inventory.itemid AS ItemID,
            SUM(Inventory.Totalunits) AS Individual_Mon         


        

Answer 1

In the past, I've solved a problem like this by creating a temporary table which will hold all dates needed:

    CREATE TABLE #AllDates (ThisDate datetime null)
    SET @CurrentDate = @StartRange

    -- insert all dates into temp table
    WHILE @CurrentDate <=  @EndRange
        BEGIN
            INSERT INTO #AllDates values(@CurrentDate)
            SET @CurrentDate = dateadd(mm, 1, @CurrentDate)
        END

Then, modify your query to join against this table:

SELECT      ALLItems.ItemId,
            SUM(COALESCE(Inventory.Qty, 0)) AS Individual_MonthQty,
            MONTH(#AllDates.ThisDate) AS Individual_MonthAsNumber,
            DATENAME(MONTH, #AllDates.ThisDate) AS Individual_MonthAsString
FROM        #AllDates
            JOIN (SELECT DISTINCT dbo.Inventory.ItemId FROM dbo.Inventory)  AS ALLItems ON 1 = 1
            LEFT JOIN Inventory ON DATEADD(dd, - DAY(Inventory.dadded) +1, Inventory.dadded) = #AllDates.ThisDate AND ALLItems.ItemId = dbo.Inventory.ItemId
WHERE       
            #AllDates.ThisDate >= @StartRange
AND         #AllDates.ThisDate <= @EndRange
GROUP BY    ALLItems.ItemId, 
            #AllDates.ThisDate

Then you should have a record for each month, regardless of whether it exists in Inventory.

Answer 2

Here's one way. This assumes that @StartRange and @EndRange fall within the same calendar year, otherwise you will get some funny results.

WITH n(n) AS 
(
    SELECT TOP 12 ROW_NUMBER() OVER (ORDER BY [object_id])
        FROM sys.objects
),
months(m, mn) AS
(
    SELECT n, DATENAME(MONTH, DATEADD(MONTH, m-1, '19000101')) 
        FROM n
)
SELECT 
    ItemID = i.itemid,
    MonthQty = COALESCE(SUM(TotalUnits), 0),
    MonthAsNumber = m.m,
    MonthAsString = m.mn
FROM
    months AS m
LEFT OUTER JOIN
    Inventory AS i
ON
    MONTH(i.dadded) = m.m
WHERE
    i.invtype = 'Shipment'
    AND i.dadded >= @StartRange
    AND i.dadded <= @EndRange
GROUP BY
    m.m, m.mn, i.itemid
ORDER BY m.m;

Answer 3

You could prepare a 'calendar' table like so:

DECLARE @d datetime
SET @d = @StartRange

DECLARE @calendar TABLE (Date datetime)

WHILE (@d <= @EndRange) BEGIN
    INSERT INTO @Calendar VALUES (@d)
    SET @d = DATEADD(month, 1, @d)
END

and then do a LEFT JOIN with your table on the month and year date parts. This way you'll always have all the months between the start and end date as rows.