Composite primary key

Question

I am working on the design of a database that will be used to store data that originates from a number of different sources. The instances I am storing are assigned unique I

Answer 1

Adding an extra ID column will leave you having to enforce TWO uniqueness constraints instead of one.

Using that extra ID column as the foreign key in other referencing tables, instead of the key that presents itself naturally, will cause you to have to do MORE joins, namely in all the cases where you need the original soruce_ID plus ID_on_source along with data from the referencing table.