Elements of a Candidate Key
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It cannot be a multipart field.
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It must contain unique values.
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It cannot contain null values.
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Its value cannot cause a breach of the organization's security or privacy rules.
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Its value is not optional in whole or in part.
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It comprises a minimum number of fields necessary to define uniqueness.
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Its values must uniquely and exclusively identify each record in the table.
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Its value must exclusively identify the value of each field within a given record.
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Its value can be modified only in rare or extreme cases.
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