The way I would do it would be to have an inventory table as well as an inventory adjustment table.
CREATE TABLE dbo.Inventory (
StockNumber INT PRIMARY KEY,
CREATE TABLE dbo.InventoryAdjustment (
AdjustmentID INT PRIMARY KEY,
And when an adjustment was made, you would do an update on Inventory
AND an Insert on InventoryAdjustment
SET Quantity = Quantity + @Adjusment
WHERE StockNumber = @StockNumber
INSERT InventoryAdjustment (StockNumber, AdjDate, AdjAmount)
VALUES (@StockNumber, GetDate(), @Adjustment)
This will allow you to see the Items and Current stock level with one table, as well as the log of individual adjustments on the item.