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Systems Analysis and Design (Shell...

11th Edition
Scott Tilley + 1 other
ISBN: 9781305494602

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BuyFindarrow_forward

Systems Analysis and Design (Shell...

11th Edition
Scott Tilley + 1 other
ISBN: 9781305494602
Textbook Problem

Describe a primary key, candidate key, secondary key, foreign key, and a combination key, Use your imagination to provide an example of each key that is not in the textbook.

Program Plan Intro

What is a primary key, candidate key, secondary key, foreign key, and a combination key? Explain with the help of an example each.

Program Explanation

Primary key: Primary key is defined as the attribute in a table which can uniquely identifies all the row of tables.

Candidate Key: Candidate key is a single attribute or a set of attributes that uniquely identify tuples or record in a database. There can be more than one candidate key for a table among which minimum candidate key can be selected as primary key. Thus, we can say the set of all potential primary key is candidate key.

Foreign key: Foreign key concept is used to create the referential integrity in relationship between two tables. A non-prime attribute in a table which is used to refer to some other table in which it acts as prime attribute is knows as foreign key.

Secondary key: Secondary key is an attribute or combination of attributes which can be used to access records. It is not necessary that secondary key values must be unique. Name field, date field, GPA field in any student table can act as secondary key.

Combination key: In a table if a single attribute or field is not able to uniquely identify every row in the table then combination of fields can be used at primary key and it is called combination key.

Let’s understand each of the above with the help of an example, consider the following tables:

Table 1: Student Table

...
Enroll No. Student Name Marks SubjectID DepartmentID Year of admission
101 John 95 501 21 1995
102 Kim 88 502 21 2005

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