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Letters for Digits

Consider the ...

Question

Consider the following relations where keys are underlined:
P(X, Y, Z) and Q (A, X)
P contain 500 records and Q contain 1500 records. X in Q is a NON-NULL attribute and a foreign key referencing to P. If a is the maximum number of records in
$P ⋈ Q and b is the minimum number of records in$
$P ⋈ Q$ .
What is the value of 2a-b________
(Where $⋈$ is a natural join)
1500

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Solution

The correct option is A 1500
$'X' in P is a key so it contain all different value and 'X' in Q is not key and referencing to P so all its record will match to 'X' in P. So there is total 1500 minimum record and also 1500 maximum records. a = 1500, b = 1500 2 a - b = 2 \times 1500 - 1500 = 1500$

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