Databases: Overview

About Structured Query Language

• SQL was first implemented in IBM's System R in the late 1970's.
• SQL is the de-facto standard query language for creating and manipulating data in relational databases.
• There are some differences, but much of SQL is standard across MS Access, Oracle, Sybase, MySQL, PostgreSQL.

• SQL is either specified by a command-line tool or is embedded into a general purpose programming language such as Cobol,"C", Pascal, or accessible via modules as in Java, PHP and Perl.
• In Perl, we use the DBI interface.
  "DBI is a database access Application Programming Interface (API) for the Perl Language. The DBI API Specification defines a set of functions, variables and conventions that provide a consistent database interface independent of the actual database being used." --Tim Bunce, the architect and author of DBI
  

• SQL is a standardized language monitored by the American National Standards Institute (ANSI) as well as by National Institute of Standards (NIST). Standards (NIST).
  • ANSI 1990 - SQL 1 standard
  • ANSI 1992 - SQL 2 Standard (sometimes called SQL-92)
  • ANSI and ISO SQL:1999, also know as SQL 3, added some object oriented concepts
  • ANSI and ISO SQL:2003, introduced XML-related features
  • ANSI and ISO SQL:2006
  • ANSI and ISO SQL:2008

• SQL has two major parts:
  1. Data Definition Language (DDL) is used to create (define) data structures such as tables and indexes,
  2. Data Manipulation Language (DML) is used to store, retrieve and update data from tables.