I don't get how something like that could ever be practical though, even on a theoretical level. Like say you ask a server for a list of all flights from airpor

I don't get how something like that could ever be practical though, even on a theoretical level. Like say you ask a server for a list of all flights from airport A to airport B. The only way this could work without making the server "know" what is happening is if the output size accommodated the list of ALL flights in ALL databases globally. So you'd have to return the client gigabytes(?) of data even though the answer probably fit in a kilobyte. Basically, fundamentally I just can't see how computation could be efficient with FHE (and this has nothing to do with the efficiency of FHE itself).