PostgreSQL is a free, open-source object-relational database system that traces directly back to the Berkeley Postgres project. According to PostgreSQL’s own history documentation, the Postgres project began in 1986 under Professor Michael Stonebraker, sponsored by DARPA, ARO, NSF, and ESL, Inc.; the first system became operational in 1987 and Version 1 was released to external users in June 1989. Postgres originally used its own query language, PostQUEL.
The shift to SQL came later. The project’s history records that “in 1994, Andrew Yu and Jolly Chen added an SQL language interpreter to POSTGRES,” replacing PostQUEL and producing an open-source descendant called Postgres95. By 1996 it was clear the name “Postgres95” would not last, and the project was renamed PostgreSQL to reflect the link between the original Berkeley Postgres and its new SQL capability. Version numbering resumed at 6.0, continuing the sequence from the Berkeley releases.
Since then PostgreSQL has been developed by a worldwide community of volunteers. Its own documentation describes it as “the most advanced open-source database available anywhere,” and it is widely valued for close adherence to SQL standards and for extensibility — the ability for users to define new data types, functions, operators, and index methods, an idea inherited from Stonebraker and Rowe’s 1986 design goals for Postgres.