PPT: Concept of keys

 Page 1


Concept of 
Keys in DBMS
Page 2


Concept of 
Keys in DBMS
Why we have Keys in DB?
Tuple Identification
A Key is an attribute or a set of attributes in a relation that identifies a tuple (record) in a 
relation.
Quick Data Access
The keys are defined in a table to access or sequence the stored data quickly and 
smoothly.
Table Relationships
They are also used to create relationship between different tables.
Page 3


Concept of 
Keys in DBMS
Why we have Keys in DB?
Tuple Identification
A Key is an attribute or a set of attributes in a relation that identifies a tuple (record) in a 
relation.
Quick Data Access
The keys are defined in a table to access or sequence the stored data quickly and 
smoothly.
Table Relationships
They are also used to create relationship between different tables.
Types of Keys in 
Database
1. Primary Key
2. Candidate Key
3. Alternate Key
4. Super Key
5. Foreign Key
6. Unique Key
An additional composite key is also there, 
which is a combination of multiple keys.
Page 4


Concept of 
Keys in DBMS
Why we have Keys in DB?
Tuple Identification
A Key is an attribute or a set of attributes in a relation that identifies a tuple (record) in a 
relation.
Quick Data Access
The keys are defined in a table to access or sequence the stored data quickly and 
smoothly.
Table Relationships
They are also used to create relationship between different tables.
Types of Keys in 
Database
1. Primary Key
2. Candidate Key
3. Alternate Key
4. Super Key
5. Foreign Key
6. Unique Key
An additional composite key is also there, 
which is a combination of multiple keys.
Primary Key
Unique & Non-NULL
Primary key is Unique & Can't 
have NULL Value
Row-Level Uniqueness
Used to maintain uniqueness in a 
table at row level.
Example
In the Employee table, we can 
choose the EmployeeID column 
for a PK.
Minimal Super Key
A primary key is the minimal 
super key. In the ER diagram, the 
primary key is represented by 
underlining the primary key 
attribute.
Ideally a primary key is composed 
of only a single attribute.
But it is possible to have a 
primary key composed of more 
than one attribute.
Page 5


Concept of 
Keys in DBMS
Why we have Keys in DB?
Tuple Identification
A Key is an attribute or a set of attributes in a relation that identifies a tuple (record) in a 
relation.
Quick Data Access
The keys are defined in a table to access or sequence the stored data quickly and 
smoothly.
Table Relationships
They are also used to create relationship between different tables.
Types of Keys in 
Database
1. Primary Key
2. Candidate Key
3. Alternate Key
4. Super Key
5. Foreign Key
6. Unique Key
An additional composite key is also there, 
which is a combination of multiple keys.
Primary Key
Unique & Non-NULL
Primary key is Unique & Can't 
have NULL Value
Row-Level Uniqueness
Used to maintain uniqueness in a 
table at row level.
Example
In the Employee table, we can 
choose the EmployeeID column 
for a PK.
Minimal Super Key
A primary key is the minimal 
super key. In the ER diagram, the 
primary key is represented by 
underlining the primary key 
attribute.
Ideally a primary key is composed 
of only a single attribute.
But it is possible to have a 
primary key composed of more 
than one attribute.
To define a field as a primary key, the following 
conditions had to be met :
Uniqueness
No two rows can have the same primary key value.
Mandatory
Every row must have a primary key value.
Non-NULL
The primary key field cannot be null.
Immutable
Value in a primary key column can never be modified or updated, if any foreign key refers to that primary key