Which criteria is useful in selecting a primary key from among several candidate keys?

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BlackTom AI · Accepted Answer

Question restatement: The prompt asks which criterion is useful when selecting a primary key from among several candidate keys.

Option 1: 'Choose concatenated keys over single attributes keys.' This suggests preferring composite (concatenated) keys rather than single-attribute keys. While composite keys can be used, they tend to be more complex, harder to manage, and may impact performance. The criterion of choosing concatenated keys is not generally considered a best practice for PK selection, especially since simplicity and stability are often valued more highly than whether a key is composite.

Option 2: 'Choose the simplest candidate key.' Simplicity is desirable for human readability and ease of use, but it is not the sole or primary criterion. A simple key could still be unstable if its values change over time, or could be inappropriate due to business rules. Therefore, while usefulness exists, this option overlooks the crucial aspect of immutability that PK values should possess.

Option 3: 'Choose the candidate most likely to not have its value changed over time.' This captures a core principle of primary key design: the key value should be stable and immutable. If a key changes, it propagates updates across foreign-key relationships and can lead to data integrity problems and costly updates. Stability is the fundamental criterion that aligns with the role of a primary key as a durable identifier.

Option 4: 'Always create a surrogate key.' Creating a surrogate key is a design strategy that can be employed, but the prompt asks for a criterion to select among candidate keys, not a universal recommendation to always use surrogates. Surrogates are an approach, not an intrinsic criterion derived from the candidate keys themselves, and they do not address the properties of the actual candidate keys.

In summary, the most defensible criterion among the options is the one that emphasizes stability of the key value over time, since a primary key should remain constant to preserve referential integrity and minimize maintenance. The other options discuss aspects related to key structure (concatenation, simplicity) or a broader design decision (surrogate keys) that do not directly answer the criterion for selecting among candidate keys in terms of data stability.

Which criteria is useful in selecting a primary key from among several candidate keys?

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