Cardinality is important and USED to arrange the data inside the database. It is related to the design part and NEED to be properly used in database. It is used in E-R diagrams and used to show the relationship between entities/tables. It has many forms like the basic is ONE to one, which associate one entity with another.

Second is one to many: which relates one entity with many entities in a table.
Third is many to many M: N that ALLOWS many entities to be related to many more.
Last is many to one: that allows the many entities to be associated with one entity.

Cardinality is important and used to arrange the data inside the database. It is related to the design part and need to be properly used in database. It is used in E-R diagrams and used to show the relationship between entities/tables. It has many forms like the basic is one to one, which associate one entity with another.

Second is one to many: which relates one entity with many entities in a table.
Third is many to many M: N that allows many entities to be related to many more.
Last is many to one: that allows the many entities to be associated with one entity.