Structured Query Language, known more popularly as SQL is an extremely popular non-procedural language that allows you to manipulate a relational database. In this regard, SQL can be categorized under two classes.

Firstly, it falls under the Data Manipulation Language (DML) class as it is used for retrieving and storing data. Secondly, it falls under the Data Design Language class (DDL) as it is used to create, alter and drop tables. Usually, SQL is used mainly as a DML, but when the requirement does pop up its features as a DDL come into play.

There are many different varieties of SQL available today. Some have proprietary SQL features which mean that they are not portable. However, most SQL versions conform to Ansi-89 and of late, Ansi-92 standards.

Data storage in SQL consists of tables that have individual rows of data. Once defined, the columns cannot be changed without affecting the rest of the rows as they are common to all rows. Indexes help the system locate records efficiently. When you consider a database with over 150,000 rows, you will begin to understand the value of an index in locating a record. To manipulate data there are four main SQL commands.

Select – retrieves information from one or more tables
Insert – stores information in a fresh row in a table
Update – allows changes to be made to existing values in one or more rows
Delete – destroys one or more rows in a table

This is a very basic introduction to a very powerful language. If you want to learn more, you should look for some tutorials on the internet which will help you get some hands-on experience on one of the most popular DMLs at the moment.