Which type of database relationship requires a separate relationship table?

A many-to-many relationship requires a separate relationship table to effectively manage the associations between two related entities. In a many-to-many scenario, each record in one table can relate to multiple records in another table, and vice versa. For instance, consider a database for students and courses where a student can enroll in multiple courses, and each course can have many students enrolled.

To keep track of which students are enrolled in which courses, a junction or relationship table is necessary. This table typically contains foreign keys referencing the primary keys of the two entities involved, thereby allowing the mapping of the various relationships between them. This structure accommodates the complexity of multiple associations, which cannot be represented adequately with just foreign keys in either of the original tables.

In contrast, one-to-one, one-to-many, and many-to-one relationships can be sufficiently handled by utilizing foreign keys within a single table instead of requiring an additional linking table.