While PostgreSQL retains the powerful object-relational data model, rich data types and easy extensibility of Postgres, it replaces the PostQuel query language with an extended subset of SQL.

PostgreSQL is an open-source descendant of some original Berkeley code. It supports SQL92 and SQL99 and offers many modern features:

    * complex queries
    * foreign keys
    * triggers
    * views
    * transactional integrity
    * multiversion concurrency control

Additionally, PostgreSQL can be extended by the user in many ways, for example by adding new

    * data types
    * functions
    * operators
    * aggregate functions
    * index methods
    * procedural languages

And because of the liberal license, PostgreSQL can be used, modified, and distributed by everyone free of charge for any purpose, be it private, commercial, or academic.