SQL and function reference?

Hey, everyone:

My first post here, so nice to meet y'all. I've recently started working
with PostgreSQL (in fact, recently started working with SQL...) and
although I'm getting off to a good start, sometimes things go bump in
the night.

In particular, I quite frequently don't know where to find answers; and
I don't want to post every bloody question here. It's slow for me, and
doubtless 99% will be FAQs or would have been solved by RTFM... if I
could find the darn FM to R.

In general, could someone point me to a good reference for SQL and
PostgreSQL commands? Immediately after subbing to this list, for
example, I saw the "extracting date from timestamp" thread which
mentions the date_trunc() function. This one function does part of what
I'd like to do in one query (thanks!) but I had not found it before.
Where can I find either a reference or a tutorial to SQL in general and
to this kind of functions?

I'll also shoot off a quick three questions if y'all don't mind, in
separate threads to make life easy on the archives.

Cheers!

--
Rodolfo J. Paiz <rpaiz@simpaticus.com>