Relational Database Management System (RDBMS) - Lecture 2, Thesis of Database Management Systems (DBMS)

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Relational Database

Management System

Lecture 2

Instructor:

Mehwashma Amir

RDBMS

RDBMS stands for Relational Database Management

System

All modern database management system like SQL, MS

SQL Server, IBM DB2, ORACLE, My-SQL and Microsoft

Access are based on RDBMS

It is called Relational Database Management System

because it is based on relational model introduced by

E.F.Codd

How it Works??

 Data is represented in terms of tuples (rows) in RDBMS.

 Relational database is most commonly used Database. It

contains number of tables and each table has its own primary

key.

 Due to a collection of organized set of tables, data can be

Accessed easily in RDBMS

WHAT IS TABLE?

 The RDBMS use tables to store data.

 A table is collection of related data entries and

contains rows and columns to store data

 A table is the simplest example of data storage in

RDBMS

CONTI..

A table is considered as convenient

representation of Relations. But a table have

duplicate value but a relation cannot have

duplicate value

WHAT IS ROW?

A row of table is called record.

It contains the specific information of

each

individual entry in a table. It is horizontal

entity.

Record/ Rows

WHAT IS NULL VALUE?

 A NULL value in a table is a value in a field that appears

to be blank, which means a field with a NULL value is a

field with no value

 It is very important to understand that a NULL value is

different than a zero or a field that contains spaces. A field

with a NULL values is one that has been left blank during

record creation

DATABASE KEYS

WHAT IS KEY?

 Keys are very important part of Relational database. They

are used to establish and identify relation between tables.

 They also ensure that each record within a table can be

uniquely identified by the combination of one or more field

within a table

 Key is a set of one or more columns whose combined

values are unique among all occurrence in a given table

TYPES OF KEY

 SUPER KEY

 CANDIDATE KEY

 PRIMARY KEY

 FOREIGN KEY

 ALTERNATIVE KEY

 COMPOSITE KEY

 SECONDARY/ ALTERNATIVE KEY

 NON-PRIME KEY

SUPER KEY

“Super key” is a set of one or more than one key

that can used as to identify a record uniquely in a

table

Example:

Primary key, Unique Key, Alternative key are subset

of Super key

CONTI…

There can be multiple candidate key in one table.

Each candidate key can work as a primary key.

PRIMARY KEY

Primary key is a candidate key that is most appropriate

to because main key of the table.

Primary key is a set of one or more fields or columns

of a table that uniquely identify a record in database