Get subquery columns in a way similar to `getTableColumns`
Keeping track manually of all subquery fields can quickly become annoying, and I'm looking for a simple helper to allow specifying fields with a pattern similar to what
getTableColumns enables. Has anyone implemented a small helper that's somewhat "battle-tested"? Here's what I have at the moment, but I'm not trusting it that much due to how naive it is and due to the necessary typecasting.