This is mostly aiming at future proofness, in case we combine multiple
fetches in a single request. Having an unextracted column would cause it
to be extracted as the first column of the next entity.

It returns all artists with at least a song from the specified musical genre

AlbumTracks now store a genre id, instead of a plaintext genre.

All mrls are added at once, there's no way to predict what the order
will be