It's not a dumb question at all. I'm pretty knowledgeable with DBs and still find it very difficult to understand how many of these front-end/pass-through engin

It's not a dumb question at all. I'm pretty knowledgeable with DBs and still find it very difficult to understand how many of these front-end/pass-through engines work. Checkout Postgres Foreign Data Wrappers. That might be the most well known approach for accessing one database through another. The Supabase team wrote an interesting piece about this recently. https://supabase.com/blog/postgres-foreign-data-wrappers-rust https://supabase.com/blog/postgres-foreign-data-wrappers-rus... You might also want to try out duckdb's approach to reading other DBs (or DB files). They talk about how they can "import" a sqlite DB in the above 0.7.0 announcement, but also have some other examples in their duckdblabs github project. Check out their "...-scanner" repos: https://github.com/duckdblabs/postgres_scanner https://github.com/duckdblabs/postgres_scanner https://github.com/duckdblabs/sqlite_scanner https://github.com/duckdblabs/sqlite_scanner