I have a database for tracking inventory which contains fixed assets (computers, printers etc.) and consumables (ink cartridges, office supplies etc). Both types have a part number. The fixed assets have serial numbers and are always a quantity of 1 the consumables don't and can have a quantity of anything.

I NEED TO HAVE A UNIQUE FIELD FOR THE PRIMARY KEY.

I can't use autonumbers. I am using multiple handheld devices for input so I can't just use a counter.

My first impulse was to combine the part number and serial number for the fixed assets and the part number and location for the consumables. This isn't a great solution because of the size of the part number and serial number (it could be up to 40 characters or more).

example:

ID     PART #      DESC         SERIAL #     LOCATION   QTY
-----------------------------------------------------------
???    1234        PC           1A2B3C       CAB1         1
???    2345        INK CART.    N/A          CAB2        12

Any advice would be greatly appreciated.