SQL: The Structured Query Language

Structured Query Language (SQL) was adopted by the American National Standards Institute (ANSI) in 1986, one year before it was adopted by the International Organisation for Standardisation (ISO). Before it was accepted and ever since adoption, SQL has been under continuous review for improvements. The Joint Technical Committee (JTC) is charged with improving SQL.

The proper pronunciation of SQL is “es queue el” although many English speaking persons still use si-kwel as in “sequel”.

Edgar F. Codd is generally recognised as the father of SQL. Codd envisioned the language as one of the first universal commercial languages. In his highly acclaimed 1970 paper entitled A Relational Model of Data for Large Shared Data Banks, Codd set forth the premise of a standardised language expressed through codes.

SQL DatabasesIBM initially developed SQL in the early 1970s. Donald D. Chamberlin, Raymond F. Boyce and Donald C. Messerly are credited with developing Structured English Query Language (SEQUEL). The language was used to manage and extract data stored in IBM’s original database management system. SEQUEL was reduced to SQL because Hawker Siddeley, a British aircraft company used SEQUEL as a trademark.

The refinement of SQL has been ongoing ever since. One of the challenges for launching SQL was that code is not completely portable among different databases.

In 1996, the National Institute of Standards and Technology (NIST) data management standards program began to certify SQL-DBMS compliance with the SQL standard. Today, vendors can self-certify that their products are SQL compliant.

SQI is generally recognised as the declarative language (4G) but the language contains definite procedural elements. The range of SQL includes data insert, query, update, delete, schema creation and modification as well as data access control.

Oracle Comes On Board

In the late 70s, Relational Software, Inc., now known as Oracle Corporation, embraced the advances made by Codd and the IBM developers. Originally, Relational Software had the idea to market the language to government agencies with huge databases. Targets were the CIA, US Navy and others.

Relational Software launched the first commercially available program, Oracle V2 in June 1979. IBM continued experimentation on their System R prototype and brought System/38, SQL/DS and DB2 to market between 1979 and 1983.

The SQL Language

Standard SQL language is divided into several language elements. These include:

Clauses – Constituent components of statements and queries.

Expressions – Expressions produce either scalar values or tables which consist of columns, rows and data.

Predicates – Predicates are used to specify conditions that can be recognised and evaluated to SQL three-valued logic (3VL) or Boolean Truth values used to limit the effects of statements and queries or to change program flow.

Queries – Queries retrieve data based on defined criteria. Queries are the most common operation of SQL.

Statements – Statements conclude with the semicolon termination signal and are not necessary for every platform but is accepted as part of the standard SQL grammar.

About Queries

The most common SQL entry is a query. A query is identified with the operation of the SELECT statement. This command set forth the retrieval of data from one or more tables or expressions.

Standard queries have no persistent effects on the database. Certain non-standard SELECT operations do have persistent effects on the data bank.
The purpose of the query is that the user can identify or describe wanted information. The query activates the database management system to plan, optimise and perform the physical operations needed to yield the desired results.

Related Articles:

What Is SQL? (SQLCourse) [http://www.sqlcourse.com/intro.html]

SQL Server Database Support (dsp) [http://www.dsp.co.uk/microsoft-support/]

About Databases (About.com) [http://databases.about.com/]

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