I don't have any experience with Hydra but I first used FDW to query external dbs about a decade ago. Also there was a pretty popular db that seemed to do a lot

I don't have any experience with Hydra but I first used FDW to query external dbs about a decade ago. Also there was a pretty popular db that seemed to do a lot of the same things sponsored by facebook, the name escapes me though. Facebook used it pretty heavily internally though.