Not really feeling sold on this.

It's called "Mastering PostgreSQL" but the site reads like it's trying to convince beginner programmers that SQL iteself is useful.

Even the case made here: http://tapoueh.org/blog/2017/11/mastering-postgresql-in-appl... seems like it would only be convincing to someone who has never had to write much SQL and also has not already had to do a pattern like that in an API call.