PostgreSQL is considered by many to be the most advanced open source database in the world (sorry mySQL), providing a wealth of features (sub-select, transactions, write-ahead logging etc) that are usually only found in commercial databases. PostgreSQL is an object-relational database management system (ORDBMS), originally developed in 1977 by the University of Berkeley and it is included by default as the main database on most *BSD systems, like FreeBSD. But in spite of its long history and extensive user base (however, it is still not as popular as the Linux-centric mySQL though), PostgreSQL suffered from a lack of comprehensive and easy-to-use documentation. "
Practical PostgreSQL" (along with 2 more PostgreSQL books, all released the last 2-3 months) fills that information void with a fast-paced guide to installation, configuration, and usage.
If you're looking for a good PostgreSQL book, get Bruce Momjian's http://www.bookpool.com/.x/r63bgfe2q6/sm/0201703319">PostgreSQL: or http://www.ca.postgresql.org/docs/aw_pgsql_book/">preview . Bruce is one of the core PostgreSQL developers.