Database Design: inventory and sales system?

Question

I need to develop a inventory and sales system.

For inventory, I need to be able to keep track of ideal stock levels, current stock levels, reorder point, cost, sell

Answer 1

I would suggest completely separating the inventory tables from the money accounting tables. For example, the example you gave I know to be ridiculous: For your average fast food restaurant a $.90 cent Coke costs about $.05-$.07 for the cup, and less than a penny for the liquid, leaving a tidy profit of $.83ish. Why do the costs have to add up to $.90?

Tables:

InventoryItems fields: InventoryItemId, Name, CurrentInventoryLevel, IdealInventoryLevel

InventoryChangeRecords fields: InventoryChangeId, InventoryItemId, Change (int)

RetailItems fields: RetailItemId, Name, Price

RetailItemMakeup fields: RetailItemId, InventoryItemId, Quantity

SaleTransactions fields: SaleTransactionId, DateTime, TotalSale

SaleTransactionItems fields: SaleTransactionId, RetailItemId, Quantity

For each sale, you should use a sproc (or trigger) to update CurrentInventoryLevel, and insert records into InventoryChangeRecords. You can easily figure out how any sale impacted inventory by joining from SaleTransaction to SaleTransactionItems to RetailItemMakeup.

If you wanted to do it in an even stronger (but IMO extraneous) manner, you could create another many-to-many table between SaleTransactionItems and InventoryChangeRecords.