What are the four types of cardinality in databases?

The four types of cardinality in databases refer to the relationships between entities in a database schema. These types are crucial for understanding how data is interconnected and for designing relational databases effectively.

The correct answer includes "One to One," "One to Many," "Many to One," and "Many to Many."

• "One to One" implies that a single record in one table corresponds to a single record in another table. For example, in a database of employees and their personal details, each employee may have exactly one personal record.

• "One to Many" means that a single record in one table can relate to multiple records in another table. This is commonly seen in relationships where, for instance, one customer can place multiple orders, thus one customer corresponds to many orders.

• "Many to One" is essentially the reverse of "One to Many," where multiple records in one table correspond to a single record in another. For instance, many orders could be linked to a single customer.

• "Many to Many" indicates that multiple records in one table can relate to multiple records in another table. A classic example is students and classes, where many students can enroll in many classes.

Understanding these cardinalities is vital for database modeling, as they