I guess it's kind of like doing all the things a join query would do, like mapping rows together, filtering, sorting, and grouping, but the final output is deno

I guess it's kind of like doing all the things a join query would do, like mapping rows together, filtering, sorting, and grouping, but the final output is denormalized into several "tables" without duplication. From what I gather, the main "win" is the size reduction in the result set, which can impact network and memory usage. Yes you can do this yourself by running multiple queries, one on each table. Presumably by paying the latency of multiple round trips.