Returning an empty result in that case may cause a more subtle failure. I would think returning an error would be a bit better as it would clearly communicate that the caller called the API endpoint incorrectly. If it’s HTTP a 400 Bad Request status code would seem appropriate.

But that query had parameter. They just fucked up parsing it

>allowing API users to return everything at once can be a problem both for our server (lots of data in RAM when fetching from the DB => OOM, and additional stress on the DB)

You can limit stress on RAM by streaming the data. You should ideally stream rows for any large dataset. Otherwise, like you say you are loading the entire thing into RAM.

I like your thought process around the ‘empty’ case. While the opposite of a filter is no filter, to your point, that is probably not really the desire when it comes to data retrieval. We might have to revisit that ourselves.