Final answer:
The types of cardinality in a database are one-to-one, one-to-many, and many-to-many. The cardinality of primary keys is one-to-one, while the cardinality of foreign keys depends on the relationship between the tables.
Step-by-step explanation:
Types of Cardinality in a Database
In a database, cardinality refers to the number of relationships between two entities or tables. There are three types of cardinality:
- One-to-One: In this type of cardinality, one record in the first table is related to only one record in the second table, and vice versa. For example, a person can have only one social security number, and each social security number can be linked to only one person.
- One-to-Many: In this type of cardinality, one record in the first table can be related to multiple records in the second table, but each record in the second table is related to only one record in the first table. For example, one customer can have multiple orders, but each order belongs to only one customer.
- Many-to-Many: In this type of cardinality, multiple records in the first table can be related to multiple records in the second table. For example, multiple students can enroll in multiple courses, and each course can have multiple students.
Cardinality of Primary Keys and Foreign Keys
A primary key is a unique identifier for a record in a table. It has a one-to-one cardinality with the table it belongs to. For example, in a table of employees, each employee has a unique employee ID as the primary key.
A foreign key is a field in a table that refers to the primary key of another table. It has a one-to-many or many-to-many cardinality depending on the relationship between the tables.
For example, in a table of orders, the customer ID is a foreign key that refers to the primary key of the customers table. Each order belongs to one customer, so the cardinality is one-to-many.