Please .
I have Database A (Archived data), Database B (Transactional data).
Both A and B do not have any timestamps in any tables.
I need to bring A (only once because it is archived data) and B with
only differentials into Database C for reporting purposes.

Currently C is cleared before loading B with differentials every night
and A is not loaded since it takes 15 hours to load.

Now I want to bring A once and leave it and then bring B every night
with differentials without clearing C.

Please suggest some solutions.

Thank You