Abstract
SQL is a database manipulation language that has been implemented by every relational database management system (DBMS) intended for multiple users, partly because it has been accepted by the American National Standards Institute (ANSI) and the International Standards Organization (ISO) as a standard query language for relational databases. This chapter presents an overview of the environment in which SQL exists. It reviews SQL history, so as to know where it came from and where it is heading. The chapter introduces the database that is used for sample queries, along with an overview of relational database terminology. Finally, it describes the way in which SQL commands are processed and the software environments in which they function. For the most part, SQL syntax does not reflect the underlying relational algebra used to process a query. However, there are a few relational algebra operations that are actually part of SQL (in particular, UNION and JOIN).
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