If it's used as an identifier to link together rows from different tables. Also known as "joining" tables. SSN (with birthdate) is a unique identifier, and so it's natural to choose as a primary/foreign key.
If it's used as an identifier to link together rows from different tables. Also known as "joining" tables. SSN (with birthdate) is a unique identifier, and so it's natural to choose as a primary/foreign key.