what is PostgreSQL?

PostgreSQL is a free object-relational database server (database management system). It offers an alternative to other open-source database systems (such as Ingres, MySQL and Firebird), as well as to proprietary systems (such as Oracle, Sybase, IBM's DB2 and Microsoft SQL Server).
PostgreSQL is not controlled by any single company, but relies on a global community of developers and companies to develop it.

advantages of PostgreSQL

• can be run on many operating systerms

• open source

• fast performance

• support and training avavilable

relevant books about PostgreSQL

• Practical PostgreSQL (O'Reilly Unix)

• PostgreSQL
• A PostgreSQL Tutorial
• Comparison of relational database management systems
• List of Relational Database Management Systems