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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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  1. 21 August, 22:27
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    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
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