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That moves your API layer to the client library you need to distribute and build for your customers in programming languages they support. There are some cases where a thick client makes sense, but usually easier to do it server side and let customers consume the API from their env, it is easier to patch the server than to ship library updates to all users.

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I think most of the discussion in this thread assumes that “customers” of the interface are other groups in the same organization using the database for a shared overarching business/goal, not external end user customers.

For external end users, absolutely provide an API, no argument here. The internal service interactions behind that API are a less simple answer, though.

It's definitely worse for external customers, of course. But it's still not that easy even for internal customers. The main problem is that usually the tables exposed are not meant to be public interfaces, so the team takes on an external dependency to their internal schema. And that other team could have completely different goals and priorities, speed and size, management and end users with different requirements. At some point the other team might start to ask the first team for adding some innocent looking fields to their internal table for them. Also first team might need to make changes to support their own service that might not be compatible with the other team. The other team making queries that are not in control of the team owning the DB, which could impact performance. If possible, it is better to agree on an API and avoid depending on internal implementations directly even for internal customers. There are always some exceptions, e.g. very close or subteams under same management and same customers could be fine. Or if the table in question was explicitly designed as a public interface, it is rare, but possible.

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