What is the purpose of a join table?

A join table serves as an intermediary that enables many-to-many relationships between two or more tables in a relational database. When two object types have a many-to-many relationship, it means that each instance of one object can be associated with multiple instances of another object, and vice versa.

To manage this complexity, a join table is created. This table contains foreign keys that reference the primary keys of the two object types it connects. By doing so, the join table effectively captures the associations between the instances of the different object types. For example, consider a scenario involving students and classes where students can enroll in multiple classes, and classes can have multiple students. The join table would store the relationships linking student IDs to class IDs, thereby allowing for effective querying of student enrollments or class rosters.

Using a join table in this way simplifies data management and querying for many-to-many relationships, making it a fundamental aspect of relational database design without altering the underlying data structures of the original tables.