Schema check

The segment of the db is to provide a lookup of different customer and supplier part numbers in comparison to "ours". So customer X uses par t no xyz, cust Y uses abc, supplier A uses 123 and we use 666, all for exactly the same part.

I had in mind -

customers, customers_partNum, suppliers, suppliers_partNum, partNum

but i'm not entirely happy with this design as suppliers can become customers, etc...

It was proposed to me that I use a vendor table with a lookup table as to whether they are a customer or supplier, and then programmatically discern the customer/supplier details dependent on the results of the lookup code and vendor ID. This design seems more code reliant rather than allowing the SQL to do the work.

partNum, vendorPartNum (includes 'Type' lookup code and customer/supplier ID), vendorType (lookup table for vendor 'Type'), customers, suppliers

If anyone has any thoughts on this, I'd be pleased to hear them.