Not to take anything away from the books on the topic, but my favorite
source is the docs that got installed with postgres
(/usr/local/pgsql/doc/html).
The index isn't great, but easily overcome:
grep -i "search phrase" /usr/local/pgsql/doc/html/* | less
Try to do that with a book. :-)
When I can't find the answer there, I search the mailing list archives
and/or google.
-heath