SQL Group and Sum By Month - Default to Zero - sql

Question

I am currently grouping and summing inventory usage by month:
SELECT Inventory.itemid AS ItemID,
SUM(Inventory.Totalunits) AS Individual_MonthQty,
MONTH(Inventory.dadded) AS Individual_MonthAsNumber,
DATENAME(MONTH, Inventory.dadded) AS Individual_MonthAsString
FROM Inventory
WHERE Inventory.invtype = 'Shipment'
AND Inventory.dadded >= #StartRange
AND Inventory.dadded <= #EndRange
GROUP BY Inventory.ItemID,
MONTH(Inventory.dadded),
DATENAME(MONTH, Inventory.dadded)
This gives me the results that I'm expecting:
ItemID Kit_MonthQty Kit_MonthAsNumber Kit_MonthAsString
13188 234 8 August
13188 45 9 September
13188 61 10 October
13188 20 12 December
Question
What must I do to return zero for months where no data exsits, like this:
ItemID Kit_MonthQty Kit_MonthAsNumber Kit_MonthAsString
13188 0 1 January
13188 0 2 February
13188 0 3 March
13188 0 4 April
13188 0 5 May
13188 0 6 June
13188 0 7 July
13188 234 8 August
13188 45 9 September
13188 61 10 October
13188 0 11 November
13188 20 12 December

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

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.

Answer 3

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;