SQL (pronounced ess-que-ell, not see'qwl, though database geeks still argue about that), is a language specifically designed with databases in mind. SQL enables people to create databases, add new data to them, maintain the data in them, and retrieve selected parts of the data. Introduced in 1970, SQL has grown and advanced over the years to become the industry standard. It is governed by a formal standard maintained by the International Standards Organization (ISO).
Various kinds of databases exist, each adhering to a different model of how the data in the database is organized.
SQL was originally developed to operate on data in databases that follow the relational model. Recently, the international SQL standard has incorporated part of the object model, resulting in hybrid structures called object-relational databases. In this chapter, I discuss data storage, devote a section to how the relational model compares with other major models, and provide a look at the important features of relational databases.
Before I talk about SQL, however, I want to nail down what I mean by the term database. Its meaning has changed, just as computers have changed the way people record and maintain information.
Today people use computers to perform many tasks formerly done with other tools. Computers have replaced typewriters for creating and modifying documents. They've surpassed electromechanical calculators as the best way to do ...