Inventory items with multiple parts

[CC]

Hi! I'm doing a orders database, and I'd also like to track inventory. Some
of our products consists of multiple inventory items, e.g. PC plus monitor.
The PCs and monitors are inventoried separately. So I need a way to show that
the inventory decreases for more the PC and the monitor when that product
code is ordered. (I have many combinations of different bundles - this is
just one.)

Someone suggested the following:
tblInventoryItems
InvID (pk)

tblMerchandiseItems
MerchID (pk)

tblMerchandiseInventory
MerchInvID (pk)
MerchID one-to-many to tblMerchandiseItems
InvID one-to-many to tblInventoryItems
InvQuantity
- Combination of MerchID & InvID can probably have a unique index.
- Single-item Merchandise will have one record in this table (InvID &
MerchIDs might even be the same)
- Merchandise with 3 Inventory components will have 3 records.
- Structure allows a "2-for-one special" MerchID, if desired.

Merchandise sales go through tblMerchandiseInventory to determine what
inventory items have been sold.
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But my questions are:
1. In tblMerchandiseInventory, do I need to have a separate pk? Can't my pk
be MerchID + InvID? Or is there a reason to have a separate pk?

2. Shouldn't InvQuantity be in tblInventoryItems? If one of my inventory
items is part of several merchandise items, and I enter InvQuantity in
tblMerchandiseInventory, then I'll be duplicating information, right?


Thank you!