If A and B are candidate keys, then AB is candidate key or not ?

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Question :

If R{abc} is a relation, f{ a->b b->a a->c b->c }, then a and b are candidate keys. What about ab ? Is it a candidate key or is it a super key or both ?

Answer :

The union between A and B is a superkey.

(A candidate key is a superkey but a superkey could be not a candidate key)

Moreover, remember that a candidate key is a particular type of superkey, so you shouldn’t worry about if it is “both” key and superkey.

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