[refset]

For anyone happy enough to consider dealing with the JVM instead of C, and Clojure instead of SQL, I think this CINQ project can deliver on much of what you're looking for here: https://github.com/wotbrew/cinq

> I just write a SQL query instead with joining with seeing the internal data representation of the software as an information system instead of bespoke code

This sounds very similar to how CINQ's macro-based implementation performs relational optimizations on top of regular looking Clojure code (whilst sticking to using a single language for everything).