SQL, a language for database management

SQL is convenient for managing large collections of data organized as lists of attributes. The classical activity of an enterprise, transactions and resources are perfectly managed by a such tool.

This is the most used language for building and using relational databases. The original name was SEQUEL that is a short for "Structured English QUEry Language", but was condensed to SQL and the full name "Structured Query Language", come then. Must be pronounced S-Q-L.
The authors of the language are Donald D. Chamberlin and Raymond F. Boyce at IBM. The System/38 implemention was sold by IBM in 1979, while the Oracle software was created by Relational Software in the same year (this firm has been renamed Oracle further). In 1982 IBM implemented SQL in DB2.
SQL becomes an ANSI standard in 1986, an ISO standard in 1987 but actual implementations are far to be standardized.
SQL 2003 added XML features to the language.

The language has several variants and various procedural extensions depending on the editors.

Features of a query language

In the relational model, queries are expressed declaratively as relations between categories of data (with "and", "or" operators mainly).

SQL relational model

The main novelty of the 2003 version is the ability to process XML. In the 2006 version is defined precisely how to store XML and access the content with queries.
2008 and 2011 versions make minor modification.

Note that the 2013 version of PostgreSQL to store JSON code in the tables and access programmatically the content.

Sample code

Hello world. 

CREATE TABLE message (text char(15));
INSERT INTO message (text) VALUES ('Hello, World!');
SELECT text  FROM message;
DROP TABLE message;

Choose articles when cost is less than 50 $. 

SELECT * FROM article  
WHERE price < 50

The main free SQL database managers are MySQL, supported by all shared hostings, SQLite for a single database, and PostgreSQL for intensive transactions.

Documents and references