Answer:
D. Each foreign key value MUST match a primary key value in another relation or the foreign key value must be null.
Explanation:
In Computer programming, integrity constraints can be defined as a set of standard rules that ensures quality information and database are maintained.
Basically, there are four (4) types of integrity constraints and these are;
1. Key constraints.
2. Domain constraints.
3. Entity integrity constraints.
4. Referential integrity constraints.
Referential integrity states that each foreign key value must match a primary key value in another relation or the foreign key value must be null.
For instance, when a foreign key in Table A points to the primary key of Table B, according to the referential integrity constraints, all the value of the foreign key in Table A must be null or match the primary key in Table B.
<em>Hence, the referential Integrity constraints ensures that the relationship between the data in a table is consistent and valid. </em>
