Chapter 3, Problem 23P

Program Plan Intro

Primary Key:

A Primary Key in a database table is a field in the table that uniquely identifies every row or record present in the database table.

Example:

Students in Universities are assigned a unique registration number.

Therefore, in a STUDENT database table, the attribute “reg_no” acts as primary key.

Foreign Key:

Foreign Key is a column in a relational database table which provides a relation between two tables. It provides a cross reference between tables by pointing to primary key of another table.

Example:

In STUDENT database table, the attribute “reg_no” acts as primary key and in COURSE database table in which the student selects his or her course, the same “reg_no” acts as foreign key for the STUDENT table.

Many to One Relationship:

When more than one record in a database table is associated with only one record in another table, the relationship between the two tables is referred as many to one relationship. It is also represented as M: 1 relationship.

One to Many Relationship:

When one record in a database table is associated with more than one record in another table, the relationship between the two tables is referred as one to many relationship. It is also represented as1: M relationship. This is the opposite of many to one relationship.

RELATIONAL DIAGRAM:

Relational Diagram is also known as Entity Relational Diagram. It is used to define the conceptual view of the database as viewed by the end user. It is used to depict the database’s main components: entities, relationships and attributes. It describes how data is related to each other.