The fact that you’d need to keep this structure in SQL and make sure it’s consistent and updated kinda proves my point.
It’s also not really relevant to my example, which involves a single level parent-child relationship of completely different models (posts and tags).
My point is that SQL works with and returns data as a flat table, which is ill fitting for most websites, which involve many parent-child object relationships. It requires extra queries to fetch one-to-many relationships and postprocessing of the result set to match the parents to the children.
I’m just sad that in the decades that SQL has been around, there hasn’t been anything else to replace it. Most NoSQL databases throw out the good (ACID, transactions, indexes) with the bad.