books/sites for someone really learning PG's advanced features?

I'm switching to PostgreSQL from MySQL. Using the SAMs book called
PostgreSQL which has been great to skim the surface of the
differerences.

I had never even heard of things like triggers, views, and foreign keys before.

Any recommended books or websites (or exercises) that would really
help someone get to know not just the basics of how these advanced
features work, but some real in-depth insight into how to USE them for
real work?

(It's always hard to get used to actually using features you never
knew existed before.)

Thanks!