An instance of relational schema $R(A,B,C)$ has distinct values of $A$ including $NULL$ values. Which one of the following is true?
They have mentioned clearly that it’s “An instance of relational schema...”
And based on the instance we cannot conclude if an attribute will be CK or NOT. May be now, at this point of time, the values are distinct but it doesn’t mean that in future also it’s going to be distinct. Also, for the same reason we cannot even conclude that it’s not the CK. It may so happen that it’s the CK. Both are possible.
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Databases: GATE CSE 1994 | Question: 3.7 (gateoverflow.in)
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