You don’t need graphql for that, modern sql databases that support json documents already support something like this.

In Postgres, either return nested json structures, or nested arrays. For an example see: https://shusson.info/post/building-nested-json-objects-with-...

Also supported by some ORMs like JOOQ: https://blog.jooq.org/nesting-collections-with-jooq-3-14s-sq...