Given an instance of the STUDENTS relation as shown as below…
2014
Given an instance of the STUDENTS relation as shown as below
\(\begin{array}{|c|c|c|c|c|} \hline \textbf {StudentID} & \textbf{StudentName} & \textbf{StudentEmail} & \textbf{StudentAge} & \textbf{CPI} \\\hline \text{2345} & \text{Shankar} & \text{shankar@math} & \text{X} & \text{9.4}\\\hline\text{1287} & \text{Swati} & \text{swati@ee} & \text{19} & \text{9.5}\\\hline\text{7853} & \text{Shankar} & \text{shankar@cse} & \text{19} & \text{9.4} \\\hline \text{9876} & \text{Swati} & \text{swati@mech} & \text{18} & \text{9.3} \\\hline \text{8765} & \text{Ganesh} & \text{ganesh@civil} & \text{19} & \text{8.7} \\\hline \end{array}\)
For \((StudentName, StudentAge)\) to be a key for this instance, the value \(X\) should NOT be equal to______.
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Correct answer: 19
Answer: X should not be 19.
Why: A key must give a unique pair value for each tuple. The instance already contains a tuple with StudentName = Shankar and StudentAge = 19 (StudentID 7853). If X were 19, the first tuple (StudentID 2345) would also have (Shankar, 19), creating a duplicate (StudentName, StudentAge) pair and violating uniqueness. Therefore X must not equal 19.
Existing tuple: StudentID 7853 → (StudentName = Shankar, StudentAge = 19).
If X = 19, tuple StudentID 2345 → (StudentName = Shankar, StudentAge = 19) would duplicate the above pair.
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