An application needs to fetch the top-3 matching sentences from a dataset of books while...

Fetching the top-3 matching sentences requires a similarity search, and balancing speed and accuracy points to approximate nearest neighbor (ANN) techniques. Option A—approximate similarity search with VECTOR_DISTANCE—uses an index (e.g., HNSW, IVF) to quickly find near-matches, ordered by distance (e.g., SELECT sentence, VECTOR_DISTANCE(vector, :query_vector, COSINE) AS score FROM books ORDER BY score FETCH APPROXIMATE 3 ROWS ONLY). The APPROXIMATE clause leverages indexing for speed, with tunable accuracy (e.g., TARGET_ACCURACY), ideal for large datasets where exactness is traded for performance.

Option B (exact search with Euclidean) scans all vectors without indexing, ensuring 100% accuracy but sacrificing speed—impractical for big datasets. Option C (“multivector” search) isn’t a standard Oracle 23ai construct; it might imply multiple vectors per row, but lacks clarity and isn’t optimal here. Option D (relational filters plus similarity) adds WHERE clauses (e.g., WHERE genre = 'fiction'), useful for scoping but not specified as needed, and doesn’t inherently balance speed-accuracy without ANN. Oracle’s ANN support in 23ai, via HNSW or IVF withVECTOR_DISTANCE, makes A the practical choice, aligning with real-world RAG use cases where response time matters as much as relevance.