Consider a relational schema S = (U, V , W, X, Y , Z) on which the following functional dependencies hold: {U → V , V W → X, Y → W, X → U} Which are the candidate keys among following options?
Pick an option to check yourself, or open the answer below.
Show answer & explanation
Correct answer: D. UYZ, VYZ, XYZ
Explanation
Y and Z never appear on a right side, so every key has YZ (YZ+ = Y, Z, W). Adding U, V or X each reaches all attributes (U → V, VW → X, X → U), giving UYZ, VYZ and XYZ.
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