That is a really interesting case. Correct me if I'm wrong, but I don't think this is a special case where you have to use `NATURAL JOIN` over `JOIN ON`. The pr

That is a really interesting case. Correct me if I'm wrong, but I don't think this is a special case where you have to use `NATURAL JOIN` over `JOIN ON`. The problem is just that the Postgres SQL grammar (maybe most/all SQL grammars) require ON or USING in a non-NATURAL join, so you have to specify the (empty) equijoin predicate list yourself, i.e. the identity value: `JOIN ON TRUE`. EDIT: I had another thought about this. I think people not designing with the relational algebra in mind is the heart of the issue, specifically w.r.t. column names. We know that namespaces are a hard problem, and a consequence of that problem is that `NATURAL JOIN` as specified in the relational algebra seems risky, or overly magick-y. It makes what might be an unfortunate coincidence (name collision) into something algebraically impactful. A foreign key join gets around the problem by keeping names and namespaces out of it. It's really doing exactly what `NATURAL JOIN` is supposed to do, but only in the subset of cases where name collisions are meaningful, not coincidental.