I have a table called Transactions
transactions ( TransactionID, CustomerID, DeviceTypeID, TransactionQuantity, TransactionDate, ManufacturerID)
TransactionID → CustomerID
TransactionID → DeviceTypeID
TransactionID → ManufacturerID
TransactionID → TransactionQuantity
TransactionID → TransactionDate
TransactionID → TransactionValue
Where transactionID is a primary key.
CustomerID DeviceTypeID ManufacturerID are all foreign keys.
DeviceTypeID and ManufacturerID are needed to tell what "product" a customer is buying.
However, the is another table "inventory" which basically has
These two keys are a composite primary key, and a number or quantity.
inventory ( DeviceTypeID, ManufacturerID, InventoryQuantity )
(DeviceTypeID, ManufacturerID) → InventoryQuantity
Basically, in the inventory, there isnt a device for every manfucaturer. Say,there arent LG boilers in the inventory. But samsung ones are there.
It seems that Transaction Quantity is dependend on DeviceTypeID, ManufacturerID. And manufactuerID is dependend on DeviceTypeID and vice versa but I could be wrong.
It looks like this is in 3NF but i am not sure. I havent seen cases anywhere discussing what happens when you include composite/compound keys in a transaction table and a primary key.
Contextually speaking none of the keys have any realtion with each other in the table.