In a relational database, such as your Blackbaud database, fields can be one-to-one or one-to-many.

A a one-to-one relationship represents a situation in which one data value can have only one associated element. A one-to-many relationship, on the other hand, can have any number of associated elements.

For example, suppose a database has the following fields specific to people in the database:

  • Social Security Number
  • Height
  • Weight
  • Favorite Foods
  • Nicknames

These data fields all describe a person. Let's examine the relationship types between the fields. For a person, there is a one-to-one relationship with Social Security Number (each person has a unique number, and cannot have two numbers). Likewise, height and weight are both one-to-one relationships, as people can have only one height and one weight. Granted, that value can change over time, but at any point in time, that person has one specific height and one specific weight.

Favorite Foods, on the other hand, is a one-to-many relationship. A person can have many favorite foods (popcorn, candy, pizza, etc.). Similarly, Nicknames is a one-to-many relationship (though people may have just one, or even none, it is possible to have several nicknames).

Typically if a field name can be said as a plural, it is most likely a one-to-many relationship.