Consider the following schema for customer: (id, name, street, city, state, zip, phone), in which customers are uniquely determined by their name and phone or by their id. How many super keys are there for this relation? Justify your answer.

Question

Computers and Technology

Fabian Hinton

21 August, 20:54

Consider the following schema for customer: (id, name, street, city, state, zip, phone), in which customers are uniquely determined by their name and phone or by their id. How many super keys are there for this relation? Justify your answer.

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Answers (1)

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Robertson · Answer 1

Super key is a set of attributes that uniquely identifies all attributes in a relation. Super keys are more than candidate key.

Explanation:

For example in the given schema where

Customer: (id, name, street, city, state, zip, phone)

We have a relation we check super keys by following dependencies

Functional Dependencies Super Key

id YES

name YES

id, name - > street, city, state, zip, phone YES

id, street - >name, city, state, zip, phone YES

id, city - >name, street, state, zip, phone YES

id, state - >name, street, city, zip, phone YES

id, phone - >name, street, state, zip, city YES

id, name, street YES

id, name, street, city YES

id, name, street, city, state YES

id, name, street, city, state, zip, phone YES

All these are uniquely identified

All these are super key but in reverse they are not super key such as

street, city, state, zip, phone->id, name No