Stock on the fly missing values with no sales - sql

Question

I have the following queries,
QryStockOnHand
SELECT QrySaleTot.Item, QrySaleTot.ProductID, [QryStockLevel].[Stock]-[QrySaleTot].[Quantity] AS StockOnHand
FROM QryStockLevel INNER JOIN QrySaleTot ON QryStockLevel.ProductID = QrySaleTot.ProductID;
QrySaleTot
SELECT TblProduct.Item, Sum(TblTotalSale.Size) AS Quantity, TblProduct.ProductID
FROM TblProduct INNER JOIN TblTotalSale ON TblProduct.[ProductID] = TblTotalSale.[ProductID]
GROUP BY TblProduct.Item, TblProduct.ProductID;
QryStockLevel
SELECT TblStock.ProductID, Sum(TblStock.StockLevel) AS Stock, TblProduct.Item
FROM TblStock INNER JOIN TblProduct ON TblStock.ProductID = TblProduct.ProductID
GROUP BY TblStock.ProductID, TblProduct.Item;
When I run the QryStockonHand and no sales of a product have been made then the porduct does not appear in the result of the query...
Sample Data
TblStock
StockID ProductID StockLevel
138 1 528
139 3 528
140 5 528
141 9 528
142 7 528
143 18 80
144 30 72
145 34 72
146 33 72
147 32 200
148 22 80
149 19 80
150 23 80
151 20 80
TblProduct
ProductID Item Price StockDelivery PriceSmall Large Small
1 Carling £2.50 528 £1.40 2 1
3 Carlsburg £2.70 528 £1.60 2 1
5 IPA £2.30 528 £1.20 2 1
7 StrongBow £2.80 528 £1.65 2 1
9 RevJames £2.45 528 £1.30 2 1
11 Becks £2.90 72 1
12 WKDBlue £2.80 72 1
13 WKDRed £2.80 72 1
14 SmirnoffIce £2.80 72 1
TblTotalSale
TotalSalesID ProductID SalePrice Day Time Size
576 1 £1.40 19/02/2012 15:34:24 1
528 1 £2.50 09/02/2012 14:44:44 2
530 1 £1.40 09/02/2012 14:44:44 1
565 1 £2.50 19/02/2012 15:34:24 2
567 1 £1.40 19/02/2012 15:34:24 1
570 3 £2.70 19/02/2012 15:34:24 2
571 3 £1.60 19/02/2012 15:34:24 1
577 3 £2.70 19/02/2012 15:34:24 2
578 3 £1.60 19/02/2012 15:34:24 1
533 3 £2.70 09/02/2012 14:44:44 2
534 3 £1.60 09/02/2012 14:44:44 1
Any Idea why... I guess it is a null thing, where it is seeing the no sales as a non existent thing, instead of a zero sales.... any idea how i could fix it?
Thanks
Sam

Answer 1

Instead of an inner join, use a left outer join, which will tell it to grab all of the rows from the left hand table on the join, instead of an inner join, which returns only rows which have values in both tables.
I don't know the QryStockLevel fields, but your query should look something like this:
SELECT QryStockLevel.Item, QryStockLevel.ProductID, [QryStockLevel].[Stock]-NZ([QrySaleTot].[Quantity],0) AS StockOnHand
FROM QryStockLevel LEFT OUTER JOIN QrySaleTot ON QryStockLevel.ProductID = QrySaleTot.ProductID;
Note the NZ function to handle a null on the Quantity when qrysaletot does not have a row.