Turn two database tables into one?

Question

I am having a bit of trouble when modelling a relational database to an inventory managament system. For now, it only has 3 simple tables:

1. Product

Answer 1

If the tables really are and always will be identical (and I have my doubts), then name the unified table something more generic, like "InventoryTransaction", and then use negative numbers for one of the transaction types: probably sales, since that would correctly mark your inventory in terms of keeping track of stock on hand.