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

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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