Thanks Bill. I guess I should be more specific so the answer can be
more ful to me So I'll be very specific...

I have a freelance site at http://www.nerdlance.com. Each project has a
"project clarification board" (PCB). Whenever there is a new post on
the PCB, I would like to send an email to everyone that has 1) posted a
bid on the project and 2) Anyone that has posted to the PCB. So it is
possible that someone can post to the PCB withought placing a bid.
Obviously, I don't want the message to be sent to the same person
twice, so I can't have duplicates. Also, I wouldn't want the email to
go to the person that just posted to the PCB, or the project owner, as
his/her message will be slightly different.

The data I'm retrieving will come from two tables. Table 1 is "bids"
and table 2 is "projectclarify". Among other fields, "bids" has the
following: bid_id, user_id, & project_id. "projectclarify" has the
these fields: clarify_id, project_id, from_id (from_id is the user_id
that posted the project).

So, is it possible to join these tables like you mentioned if the
user_id field has a different name in the second table?

An example to look at would be http://www.nerdlance.com/p67, which has
a few bids and a couple of PCB posts, though no examples of a PCB post
without a bid.

Like I mentioned, I can figure out ways to do this with two queries,
then manage the data with PHP, but I'd like to know if its possible to
get all the info I need with just one query.

Thanks!
-Dustin