Thanks for writing the code. I'm not going to accept the PR, because I believe there are easier ways around it, plus a number of other reasons.

First, as you put it, JSON is a first class citizen in most databases nowadays, so you should be able to extract the label values in your query, just as you would select values from a regular table column.

Second, if the argument is that you can't have fully dynamic labels for your metrics, that is by design. Your data should not control what is essentially your schema. E.g. you don't want to have a metric with 3 labels and another metric, with the same name, but 4 labels. (I seem to recall that the Prometheus client library would blow up if you try to do that.) Labels should be configuration controlled, not data controlled.

That being said, I did add some comments to clean up the code. And I'll leave the PR around, in case someone else is interested.