Overview and history

SQL originally developed by IBM (pronounced as sequel for Structured English QUEry Language) is way of communicating with relational database management systems. The commands are based on the algebra concepts developed by EF Codd as early as 1970.

The commands can be broadly categorised as listed below:

Query

This is the most commonly used statements among all other commands. Used for getting information from the database objects such as tables or views. This command retrieves the data in the form of a collection of rows where each row is divided into columns.

Data Manipulation Language

These commands are used to manipulate the content of a table. When issued by a client, the changes are visible only for that client untill the changes are committed to the database.

Transaction Control Language

These commands are affect the changes done by a client to the database table/s.

Data Definition Language

In most database implementations, these commands can be used to create (or modify or delete) different types of database objects such as tables, views, indexes etc.