What is the cardinality relationship?

Cardinality relationship refers to the quantitative relationship between two entities in a database or set theory, indicating how many instances of one entity can or must be associated with instances of another entity. In a relational database, cardinality can be classified into types such as one-to-one, one-to-many, and many-to-many. This concept helps in defining the structure and constraints of data relationships, ensuring data integrity and efficient querying. Understanding cardinality is crucial for designing effective database schemas.