RDBMS Introduction

RDBMS  stands for Relational Database Management System. It is the basis of SQL  and is used in all the modern database systems. A RDBMS is basically a DBMS(Database Management System )that maintains records between the tables and is based on the Relational Model by E.F. Codd.

Table:

The data in database is stored in the form of database objects known as tables. Table consist of rows and columns . It is a collection of related data items.

Emp_Id	Name	Age	Dept
01	Gpsingh	20	Programming
02	Mpsingh	19	Web desiging

Field: Field is nothing just the columns of the table. In the above table Emp_Id, Name,Age,Dept are the fields of the table.

Row: A row is also called as a record or the row of data.  A row can consist of data of different datatypes. The data in the row can have values of different fields of different datatypes . Following is a simple row from the above table.

01

Gpsingh

20

Programming

Column:

A column is a vertical entity in a table that contain all the information of the data of a specific data type. Each column has its own data type and it can store data of that particular datatype only.

Following is the example of a column from the above table        

Name

Gpsingh

Mpsingh

 

Null Value:

A null value means a value that appears blank in the database. The null value is different from the zero value or blank spaces. The zero value or blank spaces are themselves value but a null value measn that there is no value and that field in database is blank.

SQL Constraints:

Constrains means the rules that are enforced on the columns of the table. When inserting values in the database these constraints are checked to validate the entries to be stored in the database. The main benefit of constraints is that they enforce the accuracy and reliability of the database.

Types of constraints:

1.       Column Level Constraints

2.       Table Level Constraints

 Commonly used constraints in SQL:

Constraint	Purpose
NOT NULL Constraint	Ensures that a column cannot have NULL value.
DEFAULT Constraint	Provides a default value for a column when none is specified.
UNIQUE Constraint	Ensures that all values in a column are different
PRIMARY Key	Uniquely identified each rows/records in a database table.
FOREIGN Key	: Uniquely identified a rows/records in any another database table.
CHECK Constraint	The CHECK constraint ensures that all values in a column satisfy certain conditions.
INDEX	Use to create and retrieve data from the database very quickly

:

Categories of Data Integrity:

1.     Entity Integrity : It means that there cannot be any duplicate row in the table having values of all the fields same as that of some other row in the same table.

2.     Domain Integrity : Its main focus is to check for that valid data. The data to be entered in some field may be required in some range. Eg: for applying for a vacancy of a job the date of birth may be required between required within in the two yeas rangle.

3.     Referential Integrity : The rows that are being used by some other records cannot be deleted. The value of the records may be dependent on that record. So, Until the dependency exist the records cannot be deleted.

4.     User-Defined Integrity : Enforces some specific business rules that do not fall into entity, domain, or referential integrity

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