I'm using something like this for a small personal project that's only going to have a couple of users. Basically, just an app for myself and my girlfriend for all of the various restaurants, movies, recipes, tv shows, locations, etc. that we plan to go to/do at some point in the future. It's basically just a glorified todo list that uses APIs (TheMovieDataBase, OpenStreetMap, etc.) to grab additional metadata and images to present everything nicely

I want us both to be able to make notes/add ratings to each item, so the set of tables looks like this:

    - TodoItems
    - Notes
    - Ratings

Where every TodoItem can have multiple Ratings/Notes attached. Because each of the TodoItems is going to be of a different type with different metadata depending on the type of item (IMDB/TMDB id, image url, GPS location), and I want it to be extensible in future, its schema has ended up looking like this:

    CREATE TABLE TodoItems (
      id INTEGER PRIMARY KEY NOT NULL,
      kind TEXT NOT NULL,
      metadata BLOB NOT NULL
    );

With SQLite's json manipulation functions, it's actually pretty pleasant to work with. As it grows I might end up adding some indexes, but for now the performance seems like it will be fine for this very low traffic use case. And it makes deployment and backups incredibly simple.

Postgres added native support for JSON in 2012. People have been using RDBMS to store denormalized data and even as a key-value store for way longer than that. In fact, it's very hard not to do that