Explain why the REFERENCES privilege is necessary. Give an example of how it is possible to obtain partial information about the contents of a relation by creating foreign-key constraints referencing that relation.

What will be an ideal response?


Suppose Phone number is a candidate key in the Loan relation. One can then ?nd out who has loans by creating a relation, Probe, with the attribute Phone, which REFERENCES the Phone attribute in Loan. Then, by exhaustively inserting all possible phone numbers and recording which ones produce errors, such a user would ?nd out the phone numbers of all people who have loans. Reverse telephone lookup using a number of services on the Web will make it possible to also ?nd names and addresses of those people.

Computer Science & Information Technology

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Computer Science & Information Technology

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Computer Science & Information Technology