Which statement best describes a Hash Index?

Which statement best describes a Hash Index?

• A. It maps indexed values directly to row locations for O(1) exact-match lookups but does not support range queries well.
• B. It provides O(log n) exact-match lookups and supports range queries efficiently.
• C. It supports full-text search by mapping terms to documents.
• D. It is designed for multi-dimensional proximity queries.

Answer: (A)

Hash indexes map the hash of a key directly to a storage location, so exact-lookups can be performed in constant time on average. The trade-off is that hashing doesn’t preserve any order among keys, which makes range queries inefficient because you’d have to check many buckets or keys to cover the desired range. This is why a hash index shines for exact-match lookups but isn’t suitable for ranges. By comparison, other indexing methods exist for different needs: a tree-based index maintains sorted keys and supports efficient range scans, specialized inverted indexes support full-text search, and spatial indexes handle multi-dimensional proximity queries. So the statement describing constant-time exact-lookups with poor support for range queries best captures how a hash index behaves.

Hash indexes map the hash of a key directly to a storage location, so exact-lookups can be performed in constant time on average. The trade-off is that hashing doesn’t preserve any order among keys, which makes range queries inefficient because you’d have to check many buckets or keys to cover the desired range. This is why a hash index shines for exact-match lookups but isn’t suitable for ranges. By comparison, other indexing methods exist for different needs: a tree-based index maintains sorted keys and supports efficient range scans, specialized inverted indexes support full-text search, and spatial indexes handle multi-dimensional proximity queries. So the statement describing constant-time exact-lookups with poor support for range queries best captures how a hash index behaves.