If what you are looking is a general book (not necessarily just for Postgres) I can't recommend the "Use The Index, Luke"[1] tutorial, and the accompanying book

If what you are looking is a general book (not necessarily just for Postgres) I can't recommend the "Use The Index, Luke"[1] tutorial, and the accompanying book "SQL Performance Explained" by Markus Winand, enough. It doesn't go into a lot of relational theory, but it does provide a somewhat low-level description on how indices and database data are stored, and why you want to use different kind of indices in different scenarios. [1] http://use-the-index-luke.com http://use-the-index-luke.com