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Structured Query Language

DEFINITION Structured Query Language (SQL) is a programming language designed to get information out of and put it into a relational database. Queries are constructed from a command language that lets you select, insert, update and locate data. SQL is both an American National Standards Institute and International Standards Organization standard, although many databases support SQL with proprietary extensions.

By Christine McGeever
May 15, 2000 12:00 PM ET

Computerworld - The primary vehicle used for querying, reading and updating relational databases is a language called Structured Query Language, or SQL (generally pronounced sequel). Designed for asking questions about information in a database, SQL isn't a procedural language like traditional choices such as Fortran, Basic, C or Cobol, in which you write a procedure that performs one operation after another in a predefined sequence until the task is done. The procedure may be linear, loop back on itself or jump to another point or procedure. In any case, the programmer specifies the order of execution.

With SQL, however, you tell the system only what you want. It's up to the database management system to analyze the query against its own structures and figure out what operations it needs to perform to retrieve the information.

SQL is so pervasive and fundamental to accomplishing any work involving a database that virtually every application or development tool today, no matter what its own interface looks like, ends up translating queries and other commands into SQL.

Thus, a visual programming tool for developing database-enabled applications may have an appealing, object-oriented graphical interface. But once the programming is done, the system will convert all the underlying database calls and commands into SQL. This simplifies the integration of front-end and back-end systems, especially in multi-tiered client/ server applications. The only major exception to this rule is with object-oriented databases, whose structure and architecture may not be relational.

Relational Databases

In a relational database, data is separated into sets that are stored in one or more tables with the familiar row-and-column structure. Relational databases can quickly retrieve separate data items from different tables and return them to the user, or to an application, as a single unified collection of data called the result. Because the various items can be grouped according to specific relationships (such as the relationship of an employee's name to an employee's location or sales performance), the relational database model gives the database designer a great deal of flexibility in describing the relationships between data elements for any specific system. One further result is that the user may gain a greater understanding of the information in the database.

The SQL Story

The history of SQL begins in the 1970s at IBM Research Laboratory in San Jose, where E. F. Codd and others developed the relational database model that spawned the system known as DB2. As relational databases proliferated in the 1980s, SQL was codified for commercial information technology use. In 1986, the American National Standards Institute and International Standards Organization established the language's first standard.

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