Reading this, I mistook it for a slightly different idea: using these functional languages directly inside the database process, avoiding SQL altogether.

I've wanted to try that out with e.g. Roc and a reimplementation of SQLite's on-disk format. (Of course, that's a non-starter for production use, but it could be an interesting experiment to see what that programming model was like.) The database would become kind of like a library you use to build your tables and queries with.

Also, thank you for calling it a 1+n query, not an n+1 query ;)