SQL Introduction

What is SQL?

SQL is Structured Query Language, which is used for storing, manipulating and retrieving data stored in relational database.

SQL is the standard language for Relation Database System.Examples: MySQL, MS Access, Oracle, Sybase, Informix, postgres and SQL Server all use SQL .

Why to use SQL?

SQL allows users to access data in relational DBMS it allows users to describe the data.along with that users can define the data in database and manipulate the data according to their requirement and can perform various operations according to their need..More over users can embed SQL within other languages using SQL modules, libraries & pre-compilers and the most basic thing users can create and drop databases and tables as per required using simple queries. It is also possible to create views, stored procedures and functions in the database for better efficiency and proper utilization of the database. The queries like simple to learn and you will easily learn them as go proceed in this tutorial

SQL command Execution Process:

SQL Execution Process

While executing an SQL command the SQL Engine decides how to interpret the task.

Components included in the process:

Query Dispatcher, Optimization Engines, Classic Query Engine and SQL Query Engine

Types of SQL Commands:

1.       DDL - Data Definition Language

2.       DML - Data Manipulation Language:

3.       DCL - Data Control Language:

4.       DQL - Data Query Language:

4.

DDL - Data Definition Language

Command	Description
CREATE	Creates a new table, a view of a table, or other object in database
ALTER	Modifies an existing database object, such as a table
DROP	Deletes an entire table, a view of a table or other object in the database

DML - Data Manipulation Language

Command	Description
INSERT	Creates new records in the database
UPDATE	Updates existing records in the database
DELETE	Deletes a record from the database

DCL - Data Control Language:

Command	Description
GRANT	Used to grant privileges to a user
REVOKE	Used to revoke privileges from a user

DQL - Data Query Language:

Command	Description
SELECT	Retrives certain records from one or more tables in the database