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Lecture 5 1

The document provides an overview of various types of database keys essential for relational database design, including Primary Keys, Candidate Keys, Alternate Keys, Super Keys, Foreign Keys, Composite Keys, Unique Keys, Secondary Keys, and Surrogate Keys. Each key type is defined and its role in ensuring data integrity and relationships between tables is emphasized. Understanding these keys is crucial for effective database normalization and query performance.

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Afraseyab Khan
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14 views34 pages

Lecture 5 1

The document provides an overview of various types of database keys essential for relational database design, including Primary Keys, Candidate Keys, Alternate Keys, Super Keys, Foreign Keys, Composite Keys, Unique Keys, Secondary Keys, and Surrogate Keys. Each key type is defined and its role in ensuring data integrity and relationships between tables is emphasized. Understanding these keys is crucial for effective database normalization and query performance.

Uploaded by

Afraseyab Khan
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Database

Keys
By: Khalid Asad
Associate Professor
GSSC, Peshawar
Database Keys
• In a relational database, keys play an important role in
ensuring data integrity, maintaining relationships between
tables, and enforcing uniqueness.
• Understanding different types of database keys is crucial for
efficient database design, normalization, and query
performance.
2
Database Keys

• Database keys can be categorized into different types


based on their functionality.

3
Primary Key

• A Primary Key is a column (or a combination of


columns) that uniquely identifies each row in a table.

4
Primary Key

• In a relational database, the Students and Courses


tables typically have Primary Keys (PKs) to uniquely
identify each record. Below is a structured
representation of both tables with their Primary Keys:

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Primary Key

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Primary Key

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Primary Key

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Primary Key

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Primary Key

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Candidate Key

• A Candidate Key is a set of attributes that can uniquely


identify a row.
• One of the Candidate Keys is chosen as the Primary Key,
while others are Alternate Keys.

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Candidate Key

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Candidate Key

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Alternate Key

• An Alternate Key is a Candidate Key that was not


selected as the Primary Key.

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Alternate Key

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Super Key

• A Super Key is a set of one or more attributes that can


uniquely identify a row.
• Super Keys include all Candidate Keys and Primary Keys
but may have extra attributes.

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Super Key

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Super Key

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Foreign Key (FK)

• A Foreign Key is an attribute in one table that refers to


the Primary Key of another table, establishing a
relationship.

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Foreign Key (FK)

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Foreign Key (FK)

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Composite Key

• A Composite Key is a Primary Key made up of two or


more columns.

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Composite Key

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Unique Key

• A Unique Key ensures that a column's values remain


unique, but unlike the Primary Key, it can contain NULL
values.

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Unique Key

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Secondary Key

• A Secondary Key is an attribute (or a set of attributes)


that is not a Primary Key but can be used for data
retrieval because it holds unique or important
information.

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Secondary Key

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Secondary Key

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Diff. b/w Primary & Secondary Key

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Secondary Key

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Surrogate Key

• A Surrogate Key is an artificial key, usually an auto-


incremented number, used as a Primary Key when no
natural key exists.

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Surrogate Key

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Surrogate Key

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Summary Table of
Database Keys

34

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