One-to-one

What is One-to-one?

One-to-one is the most classic and easiest relationship to conceptualize. An example of this would be computer and IP addresses, or people and social security numbers. One person should only have one social security number, if one person has more than one SSN or one SSN corresponds to more than one person, then something has gone wrong. In database context, one-to-one relationship is the easiest to deal with, as there will always be one and only one exact matches. So no extra effort need to be spent on “in-between” tables or further filtering criteria such as the case in one-to-many or many-to-many relationships.