Value safety instead of type safety. It's reasonably likely to work; even if you can't trust the UUIDs to be generated by a trustworthy source, when you test the query it'll be wrong even if you accidentally join against a table that has a sufficiently similar schema.
I'm more familiar with MySQL where I don't have anything other than basic, automatically converted types.
But in Postgres, where there's more types, can I create a type that is representationally equivalent to a builtin type but not automatically convertable? So that if I say "select * from donkey left join plant on plant.id = donkey.animal" it says "error: cannot compare PlantId with AnimalId, use an explicit cast if you really want to do this". If this were possible and ergonomic, it would be better than a relatively cryptic null in the case that plants and animals have distinct (UUID) PKs.
