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Practical PostgreSQL by John C. Worsley, Joshua D. Drake

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Chapter 3. Understanding SQL

This chapter discusses the history and fundamental concepts of SQL and forms the foundation for the next chapter, which is about applying SQL with PostgreSQL. It addresses the basics of relational databases, object-related database extensions, the structure of a SQL statement, and provides an overview of PostgreSQL-supported data types, operators and functions.

Introduction to SQL

SQL, the Structured Query Language, is a mature, powerful, and versatile relational query language. The history of SQL extends back to IBM research begun in 1970. The next few sections discuss the history of SQL, its predecessors, and the various SQL standards that have developed over the years.

A Brief History of SQL

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 renamed “SQL” for legal reasons.

In 1978, methodical ...

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