What is PostgreSQL?
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PostgreSQL is an object-relational database management system ( ORDBMS ) based on POSTGRES, Version 4.2 , developed at the University of California at Berkeley Computer Science Department. POSTGRES pioneered many concepts that only became available in some commercial database systems much later.
PostgreSQL is an open-source descendant of this original Berkeley code. It supports a large part of the SQL standard and offers many modern features:
- complex queries
 - foreign keys
 - triggers
 - updatable views
 - transactional integrity
 - multiversion concurrency control
 
Also, 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 anyone free of charge for any purpose, be it private, commercial, or academic.