Cardinality refers to the relationship between tables in a database. Represented in 1:1, 1:N, and N:M, it refers to how many instances of one entity can be associated with instances of another database entity. Cardinality is important because it helps ensure the integrity and consistency of the data in the database.
It describes the number of instances of one entity that can be associated with one, none, or many instances of another entity in a database. one-to-one relationship, “1:N“ for a one-to-many relationship, and “N:M“ for a many-to-many relationship.
See also: database replication
Examples of cardinality:
- One-to-one (1:1). A relationship where one instance of an entity is associated with only one instance of another entity. For example, one employee is assigned to one office location.
- One-to-many (1:N). This refers to a relationship where one instance of an entity is associated with one or more instances of another entity. For example, one department can have many employees, but each employee can only belong to one department.
- Many-to-many (N:M). This refers to a relationship where one or more instances of an entity can be associated with one or more instances of another entity. For example, many students can be enrolled in many courses, and each course can have many students. In order to represent a many-to-many relationship in a relational database, a junction table or associative table is often used to connect the two entities.