i worked with the supabase team on mpc for their company. multi-party computation: several parties should be able to evaluate a function over private inputs and learn only what the protocol allows.
that is the same family of questions i read at iitk. secret sharing, rounds, abort, what a party can infer from timing. here it had to sit on a real postgres stack instead of a paper protocol.
the interesting part is the join. the database still has rows, policies, and a session, and the computation still has shares and a threat model, so neither side gets to pretend the other is simple.