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Questions and Answers
What does an entity constraint ensure in a relational data model?
What does an entity constraint ensure in a relational data model?
- Every relation has a primary key and the primary key attributes cannot be NULL (correct)
- Every attribute has a NOT NULL constraint
- Every relation has a foreign key and the foreign key attributes cannot be NULL
- Every attribute has a unique constraint
What does a domain constraint ensure?
What does a domain constraint ensure?
- Values of an attribute must be from different domains
- Values of an attribute must be NULL
- Values of an attribute must be unique
- Values of an attribute must be from the same domain (correct)
What is the primary function of a primary key in a relational data model?
What is the primary function of a primary key in a relational data model?
- Uniquely identify tuples (correct)
- Support entity constraints
- Enforce domain constraints
- Ensure referential integrity
What is the purpose of a referential constraint in a relational database?
What is the purpose of a referential constraint in a relational database?
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Why is it important for a primary key to have non-NULL attributes?
Why is it important for a primary key to have non-NULL attributes?
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