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Q.

The set of attributes X ⊆ Schema (R) is a super key for relation schema R only if :

A For all relations r over R the number of tuples in projection over X of r is the same as the number of tuples in r
B All attributes of X are having non null values
C All attributes of X are having unique values
D None of the above
Answer & Explanation
Option: [C]

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