PostgreSQL has benefited well from its long history. Today, PostgreSQL is one of the most advanced database servers available. Here are a few of the features found in a standard PostgreSQL distribution:
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Object-relational In PostgreSQL, every table defines a class. PostgreSQL implements inheritance between tables (or, if you like, between classes). Functions and operators are polymorphic.
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Standards compliant PostgreSQL syntax implements most of the SQL92 standard and many features of SQL99. Where differences in syntax occur, they are most often related to features unique to PostgreSQL.
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Open source An international team of developers maintains PostgreSQL. Team members come and go, but the core members have been enhancing PostgreSQL's performance and feature set since at least 1996. One advantage to PostgreSQL's open-source nature is that talent and knowledge can be recruited as needed. The fact that this team is international ensures that PostgreSQL is a product that can be used productively in any natural language, not just English.
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Transaction processing PostgreSQL protects data and coordinates multiple concurrent users through full transaction processing. The transaction model used by PostgreSQL is based on multi-version concurrency control (MVCC). MVCC provides much better performance than you would find with other products that coordinate multiple users through table-, page-, or row-level locking.
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Referential integrity PostgreSQL implements complete referential integrity by supporting foreign and primary key relationships as well as triggers. Business rules can be expressed within the database rather than relying on an external tool.
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Multiple procedural languages Triggers and other procedures can be written in any of several procedural languages. Server-side code is most commonly written in PL/pgSQL, a procedural language similar to Oracle's PL/SQL. You can also develop server-side code in Tcl, Perl, even bash (the open-source Linux/Unix shell).
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Multiple-client APIs PostgreSQL supports the development of client applications in many languages. This book describes how to interface to PostgreSQL from C, C++, ODBC, Perl, PHP, Tcl/Tk, and Python.
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Unique data types PostgreSQL provides a variety of data types. Besides the usual numeric, string, and data types, you will also find geometric types, a Boolean data type, and data types designed specifically to deal with network addresses.
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Extensibility One of the most important features of PostgreSQL is that it can be extended. If you don't find something that you need, you can usually add it yourself. For example, you can add new data types, new functions and operators, and even new procedural and client languages. There are many contributed packages available on the Internet. For example, Refractions Research, Inc. has developed a set of geographic data types that can be used to efficiently model spatial (GIS) data.
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