Relationship Models | Database Design | Teradata Vantage - One-to-One Relationships - Teradata Vantage - Analytics Database

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:

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.