SQL

• SQL (pronounced as "ess-que-el") stands for Structured Query Language.
• SQL is an ANSI (American National Standards Institute) standard.
• SQL is used to communicate with a database.
• SQL retrieves and modifies the data in the database.
• It is a very important tool used with relational database management systems like Oracle, Sybase, Microsoft SQL Server, Access, Ingres, etc.

Although SQL is an ANSI standard, there are many extentions and variations of SQL, such as Oracle Corporation's PL/SQL or Sybase, IBM's SQL PL (SQL Procedural Language) and Microsoft's Transact-SQL but the standard SQL commands such as "Select", "Insert", "Update", "Delete", "Create", and "Drop" are still compatible to comply with the ANSI standards.

SQL is not case sensitive.

Standard SQL statements can be subdivided into 4 distinct groups which are shown below:

Group	Statements
DQL (Data Query Language)	Select
DML (Data Manipulation Language)	Delete, Insert, Update
DDL (Data Definition Language)	DROP, TRUNCATE, CREATE, ALTER
DCL (Data Control Language)	REVOKE,GRANT

A look at relational database
Since SQL is used to communicate with the database so lets see what a relational database actually is. A relational database system consists of one or more objects called tables which hold the data. Each table has a unique name. A table is made up of rows and columns.
Lets take a look at this example:

users
first_name	last_name	SSN	age
Mike	Peter	343340909	30
Adam	Sandler	313344119	31
Nam	Sam	243341909	34
Neil	Grigorian	843340900	40
John	Russel	543241507	20

This is a table named "users" and "first_name", "last_name", "SSN" and "age" are the columns. The rows, "Mike", "Adam" etc. contain the data.