Introduction to SQL language

SQL is a domain specific programming language designed to manage data stored in a relational database management system (RDBMS). It can also be used in Relational Data Stream Management Systems (RDSMS), or in “not-only SQL” (NoSQL) databases.

SQL- Sub Languages

1. Data Definition Language (DDL): to create and modify the structure of the database.
   The data definition language deals with the schema creation and modification e.g., CREATE TABLE statement allows you to create a new table in the database and the ALTER TABLE statement changes the structure of an existing table.
2. Data Manipulation Language (DML): to perform Read, Insert, Update and Delete operations on the data of the database.
   The data manipulation language provides the constructs to query data such as the SELECT statement and to update the data such as INSERT, UPDATE, and DELETE statements.
3. Data Control Language (DCL): to control the access of the data stored in the database.
   The data control language consists of the statements that deal with the user authorization and security such as GRANT and REVOKE statements.

SQL History and Standard

SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Edgar F. Codd in the early 1970s.

SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987. New versions of the standard were published in 1989, 1992, 1996, 1999, 2003, 2006, 2008, 2011, and most recently, 2016.

SQL Dialect

The users requests new features and capabilities that do not exist in the SQL standard yet, therefore, even with the SQL standard in place, there are many SQL dialects in various database products.

Because ANSI and ISO have not yet developed these important features, RDBMS vendors are free to invent their own new syntax structure.

The following are the most popular dialects of SQL:

• PL/SQL or procedural language/SQL is developed by Oracle for the Oracle Database.
• T-SQL or Transact-SQL is developed by Microsoft for Microsoft SQL Server.
• PL/pgSQL or Procedural Language/PostgreSQL that consists of SQL dialect and extensions implemented in PostgreSQL
• MySQL(acquired by ORACLE) has its own procedural language since version 5.