16. selectivity

DBMS Published 30 Sept 2026 Updated 30 Sept 2026 0 Views Verified

Why is a highly selective predicate often useful for an index?

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Answer & Explanation

4 Answers

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Option A

It disables WHERE clauses.

Additional Explanation

This option is incorrect for the stated requirement.

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Option B

A selective predicate matches relatively few rows, so an index can reduce the amount of data the engine must examine.

Additional Explanation

Correct implementation. Prefer parameterized queries in application code, validate affected rows for UPDATE/DELETE, and use transactions for related writes.

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Option C

It forces a full table scan.

Additional Explanation

This option is incorrect for the stated requirement.

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Option D

It guarantees zero disk usage.

Additional Explanation

This option is incorrect for the stated requirement.