"So then where is the open source version / extension to Postgres?" As a concrete example I like the way in the datomic schema you can eliminate bridge tables

"So then where is the open source version / extension to Postgres?" As a concrete example I like the way in the datomic schema you can eliminate bridge tables for many-many relationships using :db/cardinality :db.cardinality/many and then you store or get a vector. There should be a way to have a super-SQL middleware compatible with any language bindings including a bare CLI that eats "SQL plus some cardinality" and behind the scenes implements the bridge table manipulations. Don't repeat yourself and all that, and many/many tables are kinda repetitive. There doesn't seem to be anything remotely like that out there.