SQL Tutorial

SQL is not a database management system, but it is a query language which is used to store and retrieve the data from a database or in simple words SQL is a language that communicates with databases.

This SQL tutorial helps you learn SQL in simple and easy steps so that you can start your database programming quickly. It covers most of the important concepts related to SQL for a basic to advanced understanding of SQL and to get a feel of how SQL works.

Why to Learn SQL?

SQL (Structured Query Language) is a MUST for the students and working professionals to become a great Software Engineer specially when they are working in Software Development Domain. SQL is the most common language used almost in every application software including banking, finance, education, security etc. to store and manipulate data.

SQL is fairly easy to learn, so if you are starting to learn any programming language then it is very much advised that you should also learn SQL and other Database related concepts to become a complete Software Programmer. There are many good reasons which makes SQL as the first choice of any programmer:

SQL is the standard language for any Relational Database System. All the Relational Data Base Management Systems (RDBMS) like MySQL, MS Access, Oracle, Sybase, Informix, Postgres and SQL Server use SQL as their standard database language.

Also, software industry is using different dialects of SQL, such as −

• MS SQL Server using T-SQL,
• Oracle using PL/SQL,
• MS Access version of SQL is called JET SQL (native format) etc.

Applications of SQL

SQL is one of the most widely used Query Language over the databases. SQL provides following functionality to the database programmers:

• Execute different database queries against a database.
• Define the data in a database and manipulate that data.
• Create data in a relational database management system.
• Access data from the relational database management system.
• Create and drop databases and tables.
• Create and maintain database users.
• Create view, stored procedure, functions in a database.
• Set permissions on tables, procedures and views.

Audiences

This SQL tutorial is prepared for beginners to help them understand the basic as well as the advanced concepts related to SQL languages. This tutorial will give you enough understanding on the various concepts of SQL along with suitable examples.

Prerequisites

Before you start practicing with various types of SQL examples given in this tutorial, I am assuming that you are already aware about what is a Database, especially the basics of RDBMS and associated concepts.

SQL - Overview

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What is SQL?

SQL is a language to operate databases; it includes Database Creation, Database Deletion, Fetching Data Rows, Modifying & Deleting Data rows, etc.

SQL stands for Structured Query Language which is a computer language for storing, manipulating and retrieving data stored in a relational database. SQL was developed in the 1970s by IBM Computer Scientists and became a standard of the American National Standards Institute (ANSI) in 1986, and the International Organization for Standardization (ISO) in 1987.

Though SQL is an ANSI (American National Standards Institute) standard language, but there are many different dialects of the SQL language like MS SQL Server is using T-SQL and Oracle is using PL/SQL.

SQL is the standard language to communicate with Relational Database Systems. All the Relational Database Management Systems (RDMS) like MySQL, MS Access, Oracle, Sybase, Informix, Postgres and SQL Server use SQL as their Standard Database Language.

Why SQL?

SQL is widely popular because it offers the following advantages −

• Allows users to access data in the relational database management systems.

• Allows users to describe the data.

• Allows users to define the data in a database and manipulate that data.

• Allows to embed within other languages using SQL modules, libraries & pre-compilers.

• Allows users to create and drop databases and tables.

• Allows users to create view, stored procedure, functions in a database.

• Allows users to set permissions on tables, procedures and views.

A Brief History of SQL

• 1970 − Dr. Edgar F. "Ted" Codd of IBM is known as the father of relational databases. He described a relational model for databases.

• 1974 − Structured Query Language (SQL) appeared.

• 1978 − IBM worked to develop Codd's ideas and released a product named System/R.

• 1986 − IBM developed the first prototype of relational database and standardized by ANSI. The first relational database was released by Relational Software which later came to be known as Oracle.

• 1987 − SQL became the part of the International Organization for Standardization (ISO).

How SQL Works?

When you are executing an SQL command for any RDBMS, the system determines the best way to carry out your request and SQL engine figures out how to interpret the task.

There are various components included in this process. These components are −

• Query Dispatcher
• Optimization Engines
• Classic Query Engine
• SQL Query Engine, etc.

A classic query engine handles all the non-SQL queries, but a SQL query engine won't handle logical files. Following is a simple diagram showing the SQL Architecture −

SQL Basic Commands

The standard SQL commands to interact with relational databases are CREATE, SELECT, INSERT, UPDATE, DELETE and DROP. These commands can be classified into the following groups based on their nature −

DDL - Data Definition Language

S.N.	Command & Description
1	CREATE Creates a new table, a view of a table, or other object in the database.
2	ALTER Modifies an existing database object, such as a table.
3	DROP Deletes an entire table, a view of a table or other objects in the database.

DML - Data Manipulation Language

S.N.	Command & Description
1	SELECT Retrieves certain records from one or more tables.
2	INSERT Creates a record.
3	UPDATE Modifies records.
4	DELETE Deletes records.

DCL - Data Control Language

S.N.	Command & Description
1	GRANT Gives a privilege to user.
2	REVOKE Takes back privileges granted from user.