> Imagine you’re fetching 100 authors and each had 1000 articles, would you rather a) fetch mxn Cartesian product or b) ask the DB to send you a json aggregation where each author has a 1000 articles?

I would be surprised if the DB performed better with an aggregation than just returning the results. Assuming you have reasonable indices, it’s a trivial join.

Network latency, maybe. Assuming 20 bytes per name, with no compression that’s an extra 2 MB.

You could write the query with a CONCAT as a subquery as a poor man’s aggregation, but then you’re very much at the mercy of the planner deciding to do all of that in one pass. I’m not sure that it would. On mobile, or else I’d check.