What are the three primary types of relationships that can exist between entities in a database?

The three primary types of relationships that can exist between entities in a database are one-to-one, one-to-many, and many-to-many relationships.

In a one-to-one relationship, a single record in one entity is associated with a single record in another entity. This is used when each instance of an entity is unique and corresponds directly with another instance.

In a one-to-many relationship, a single record in one entity can be associated with multiple records in another entity. This is one of the most common relationships found in relational databases; for example, one customer may have multiple orders, but each order is linked to only one customer.

The many-to-many relationship is more complex, allowing multiple records in one entity to relate to multiple records in another entity. This is often implemented through a junction or linking table that contains foreign keys pointing to the primary keys of both entities involved, such as students enrolling in multiple courses while courses can have multiple enrolled students.

Other options mentioned do not accurately represent the standard types of relationships recognized in relational database design. For example, hierarchical relationships and the concepts of binary, tertiary, and quaternary relationships do not apply in the same context as these core relationship types, which are foundational to database normalization and structuring.