Access SQL query inner join & sum with null - sql

Question

Tables: Items, Purchases, QuoteLines.
Items has fields ItemID, ItemName, IsActive
Purchases has fields ItemID, QtyPurchased
QuoteLines has fields ItemID, NegQty, IsSold
The goal is to select all ItemID's where IsActive=yes then sum all QtyPurchased and subtract only the NeqQty where IsSold=yes
I have tried:
SELECT Items.ItemID, Items.ItemName, IIF(NegQTY=NULL, SUM(QtyPurchased), SUM(NegQty+PurchasedQty)) AS Inv_Qty
FROM Purchases, Items, QuoteLines
WHERE Purchases.ItemID=Items.ItemID AND Items.ItemID=QuoteLines.ItemID
GROUP BY Items.ItemID, Items.ItemName;
This results in "your query does not include the specified expression IIF(NegQTY=NULL, SUM(QtyPurchased), SUM(NegQty+PurchasedQty))"
I also tried an inner join between tblItems and tblPurchases to get the PurchasedQty then a second inner join between tblItems and tblQuoteLines to get only the SoldQty, then a left inner join between the PurchasedQty and SoldQty to get InventoryQty, this however gave the right value for items that existed in both PurchasedQty and SoldQty, but for items that only existed in PurchasedQty it returned NULL.

Answer 1

Consider using saved queries to calculate the total units purchased and the total units sold, then use those saved queries in the query that calculates the current inventory.
Total Units Purchased
Create a saved query named [TotalPurchasedByItemID]
SELECT
Items.ItemID,
Sum(Purchases.QtyPurchased) AS SumOfQtyPurchased
FROM
Items
INNER JOIN
Purchases
ON Items.ItemID = Purchases.ItemID
WHERE (((Items.IsActive)=True))
GROUP BY Items.ItemID;
Total Units Sold
Create a saved query named [TotalSoldByItemID]
SELECT
Items.ItemID,
Sum(QuoteLines.NegQty) AS SumOfNegQty
FROM
Items
INNER JOIN
QuoteLines
ON Items.ItemID = QuoteLines.ItemID
WHERE (((Items.IsActive)=True) AND ((QuoteLines.IsSold)=True))
GROUP BY Items.ItemID;
Current Inventory
SELECT
Items.ItemID,
Items.ItemName,
Nz([SumOfQtyPurchased],0)-Nz([SumOfNegQty],0) AS Inv_Qty
FROM
(
Items
LEFT JOIN
TotalPurchasedByItemID
ON Items.ItemID = TotalPurchasedByItemID.ItemID
)
LEFT JOIN
TotalSoldByItemID
ON Items.ItemID = TotalSoldByItemID.ItemID
WHERE (((Items.IsActive)=True));