The relational model, from which SQL draws much of its conceptual core, was formally defined in 1970
by Dr. E. F. Codd, a researcher for IBM, in a paper entitled
A Relational Model of Data for Large Shared Data Banks
.
This article generated a great deal of interest in both the feasibility and
practical commercial application of such a system.
In 1974 IBM began the System/R project and with the work of Donald Chamberlin and others, developed SEQUEL,
or
Structured English Query Language
. System/R was implemented on an IBM prototype called
SEQUEL-XRM in 1974–75. It was then completely rewritten in 1976–1977 to include multi-table and
multiuser features. When the system was revised it was briefly called "SEQUEL/2," and then re-named "SQL" for legal reasons.
In 1978, methodical testing commenced at customer test sites. Demonstrating both the
usefulness and practicality of the system, this testing proved to be a success for IBM. As a result, IBM began to
develop commercial products that implemented SQL based on their System R prototype, including SQL/DS (introduced
in 1981), and DB2 (in 1983).
Several other software vendors accepted the rise of the relational model and announced SQL-based
products. These included Oracle (who actually beat IBM to market by two years by releasing their first commercial
RDBMS, in 1979), Sybase, and Ingres (based on the University of California's Berkeley Ingres
project).
Note: PostgreSQL's name is, as you might have guessed, a play on the name Ingres. Both PostgreSQL and
Ingres trace their roots back to the UC Berkeley's Ingres RDBMS system.
