Discussion
When the values in one or more attributes being used as a foreign key must exist in another set of one or more attributes in another table, we have created a(n):
Answer: C
Correct answer: referential integrity constraint.
A referential integrity constraint requires that every value appearing in a foreign key already exist as a key value in the referenced relation. It is what prevents an order from referring to a customer who does not exist, and it is enforced by the database rather than by the application. Normal forms and anomalies concern the structure of a single relation.
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