Consider the relation Emp–Dept with SSN as key. Which of the following…
2018
Consider the relation Emp–Dept with SSN as key. Which of the following operation(s) is/are invalid?
- A.
Inserting an employee without name and address
- B.
Inserting an employee with only SSN
- C.
Inserting a department with no employee
- D.
Inserting an employee without SSN
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Correct answer: D
In the given relation, SSN is the primary key. A primary key cannot be NULL and must uniquely identify each employee. (i) Employee without name and address → Valid (attributes can be NULL unless constrained).
(ii) Employee with only SSN → Valid (primary key is present).
(iii) Department with no employee → Valid (no constraint violation given).
(iv) Employee without SSN → Invalid, because primary key (SSN) cannot be NULL.
Hence, the invalid operation is (iv).
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