The name of a field in the relation which is part of a foreign
    key. This name can appear only once in the referencing
    definition, and must correspond to a field having the same
    ordinal position in any list of referenced-fields. The names
    can be different but the fields must be of the same data type,
    length, and scale.

    At the relation level, a constraint can have one or more
    referencing-field-names that correspond to a matching list of
    referenced-field-names.