For those interested in learning more about PostreSQL, I'd recommend the book by the author of this tool[1]. It's bee a great resource for me. It's a great introduction to SQL with a focus on postgres.

(FWIW, it was called "Mastering PostgreSQL" when I bought it, but as far as I can tell, the site I linked is just an updated version).

1: https://theartofpostgresql.com/