Cardinality Ratio in DBMS

January 27, 2023

Cardinality Ratio in DBMS

On this page, we will learn about the Cardinality Ratio in DBMS.

Cardinality tells how many times the entity of an entity set participates in a relationship
There are 4 types of cardinalities
- One to one
- One to many
- Many to one
- Many to many

1. One to one cardinality

When a single instance of an entity is associated with a single instance of another entity, then it is called a one to one cardinality
Here each entity of the entity set participates only once in the relationship.

Example for one to one cardinality : Assume that the only male can be married to only one female and one female can be married to only one male, this can be viewed as one to one cardinality

2. One-to-Many cardinality

When is a single instance of an entity is associated with more than one instance of another entity then this type of relationship is called one to many relationships
Here entities in one entity set can take participation in any number of times in relationships set and entities in another entity set can take participation only once in a relationship set.

Example for one to many cardinalities For example in the Real-world, many students can study in a single college but the student cannot apply to more than one college at the same time

What is Database

Participation Constraint

Introduction Normalisation

Data Models

Cardinality

3. Many-to-one cardinality

When entities in one entity set can participate only once in a relationship set and entities in another entity can participate more than once in the relationship set, then such type of cardinality is called many-to-one

Example for many to one cardinality In real time a student takes only one course but a single course can be taken by any number of students. so many to one relationship is observed here

It means that one course can be taken by any number of students but only one course can be allotted to one student

4. Many-to-many cardinality

Here more than one instance of an entity is associated with more than one instance of another entity then it is called many to many relationships
In this cardinality, entities in all entity sets can take participate any number of times in the relationship cardinality is many to many.

Example for many to many cardinality In the Real world assume that a student can take more than one course and the single course can be taken by any number of students this relationship will be many to many relationship

Prime Course Trailer

Related Banners

Get PrepInsta Prime & get Access to all 200+ courses offered by PrepInsta in One Subscription

Get over 200+ course One Subscription

Courses like AI/ML, Cloud Computing, Ethical Hacking, C, C++, Java, Python, DSA (All Languages), Competitive Coding (All Languages), TCS, Infosys, Wipro, Amazon, DBMS, SQL and others

Cardinality Ratio in DBMS