17.10 - One-to-Many Relationships - Advanced SQL Engine - Teradata Database

Teradata Vantageā„¢ - Database Design

Product
Advanced SQL Engine
Teradata Database
Release Number
17.10
Published
July 2021
Last Update
2021-07-27
Content Type
User Guide
Publication ID
B035-1094-171K
Language
English (United States)
Last Update
2021-07-27

Assume two entities, A and B.

A 1:M relationship exists between entity A and entity B when each occurrence of entity A is related to 0, 1, or more occurrences of entity B, while each occurrence of entity B is related to at most one occurrence of entity A.

1:M relationships are commonly seen in real world situations. For example, each department has many employees, but each employee has only one department.

1:M relationships are graphed as follows:



Modeling 1:M Relationships

1:M relationships are modeled by placing the primary key of entity A as a foreign key component of entity B.

Example

Because 1:M relationships are asymmetric, the entity A key must be placed in entity B. The reciprocal relationship does not model the same E-R relationship.