I'm a little bit confused about DB System version and Database version when using OCI DB service.
E.g. for both the DB System and the Database (21c) I see:
Latest patch available:
21.12.0.0.0

However, you can apply the patches independently.
So, how do these two work together?
Can you really apply the patches independently? And of course: if not, why are there there two processes to upgrade instead of one?
Is there an order in applying the patches?
Thanks for any insight.