Relationship Models | Database Design | Teradata Vantage - 17.10 - One-to-One Relationships - Advanced SQL Engine - Teradata Database

Teradata Vantageā„¢ - Database Design

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

Assume two entities, A and B.

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

1:1 relationships are not commonly seen in real world situations.

1:1 relationships are graphed as follows:


One-to-one relationship example

Modeling 1:1 Relationships

1:1 relationships are modeled by placing the primary key of entity A as a foreign key component of entity B with no duplicates allowed. Because the relationship is symmetrical, you could just as well place the primary key of entity B as a foreign key component of entity A.

Guideline for Placing the Foreign Key

Place the foreign key in whichever entity minimizes or eliminates the possibility of nulls.

Example

Because of the symmetry of 1:1 relationships, the following entity pairs both model the same relationship:


Entity pairs in one-to-one relationship