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What is Çardinality in Database


What is Çardinality in Database



Çardinality:

1) It defines the number of entities in one entity set, which can be associated with the
number of entities of other set via relationship set. (No of rows)
2) There are the following types of mapping of cardinalities.
One entity from entity set A can be associated with at
most one entity of entity set B and vice versa.


One-to-Many: .

1) One entity from entity set “A” can be associated with more than one entities of entity set “B”.
2) However an entity from entity set “B” can be associated with at most one entity.

Many-to- One

1)More than one entities from entity set “A” can be associated with at most one entity of entity set “B”.
2) However an entity from entity set “B” can be associated with more than one entity from entity set “A”.

Many-to-Many:

1) One entity from entity set “A” can be associated with more than one entities of entity set “B”.
2) Similarly, an entity from entity set “B” can be associated with more than one entity from entity set “A”.

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