Guideline for Placing the Foreign Key - Teradata Database

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:

A		B			A			B
A_Key		B_Key	A_Key		A_Key	B_Key		B_Key
PK		PK	FK, ND		PK	FK, ND		PK
A1		B1	A1		A1	B1		B1
A2		B2	A3		A2	B5		B2
A3		B3	A5		A3	B2		B3