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.