15.00 - Many-to-Many Relationships - Teradata Database

Teradata Database Design

Teradata Database
User Guide

Many-to-Many Relationships

Assume two entities, A and B.

A M:M relationship exists between entity A and entity B when each occurrence of entity A is related 0, 1, or many occurrences of entity B and each occurrence of entity B is related to 0, 1, or many occurrences of entity A.

Somewhat more formally, Date defines M:M relationships as follows: “Let A and B be sets, not necessarily distinct. Then a many-to‑many correspondence from A to B is a rule that pairs each element of A with at least one element of B and each element of B with at least one element of A. Equivalently, we might just say the many-to-many correspondence is that pairing itself.” (2006, page 17).

M:M relationships are commonly seen in real world situations.

M:M relationships are graphed as follows: