A proper join is the right answer. But, it's not always possible to make those run well. [1] A "client side join" in the right situation can be much better, but then you probably want to do a 1+1 rathet than N+1. Do the first query to get the ids for the second query, and then construct the second query with IN or UNION depending on what works best for you database. UNION likely bloats your query string, but I've seen plenty of situations where UNION is gobs faster than IN.

Alternately, if you can separate query issuance from result parsing, you can make N+1 palletable. Ex, do your query to get the ids, wait for the results, loop and issue the N queries, then loop and wait for results in order. That will be two-ish round trips rather than N+1 round trips. But you have to search to find database apis that allow that kind of separation.

[1] You can almost always express the query you want in SQL, but that doesn't mean it will have a reasonable runtime. Sometimes server side join and client side join have about the same runtime... if it's significant and you have the usual case where clients are easier to scale than database servers, it might be worthwhile to have the join run on the client to reduce server load.