I began learning PostgreSQL a couple of years ago, having worked previously with Paradox. I would agree with a previous responder that the Douglas & Douglas book "PostgreSQL: the comprehensive guide to building, programming, and administering PostgreSQL databases" 2nd ed. is a good book. The shortcoming I noted (and I wrote an e-mail to the publisher about) was that it doesn't have a section on Rules (an important PostgreSQL feature). Really, I think the documentation that comes with PostgreSQL is excellent - it even has a pretty good section on SQL, so I would start simply by reading the program manual. I would agree there are a lot of books on SQL, even in the "For Dummies" series.
Regarding database design, two books come to mind. G. Powell "Beginning database design" published by Wiley in 2005 and the (classic?) "Database design for mere mortals" 2nd ed. by M. J. Hernandez, published by Pearson Education in (I think) 2003.
As you begin working with PostgreSQL, I think you will find these Internet forums to be quite helpful. There is a great bunch of people who are very willing to help.
Michael Schmidt