Reviewed by Aditya Kumar · Last reviewed 2026-03-24
Find users who listened to similar artists but not target: SELECT u.user_id FROM user_listens u JOIN artist_fans a ON u.artist_id = a.artist_id WHERE a.artist_id = :target_artist_id AND u.user_id NOT IN (SELECT user_id FROM user_listens WHERE artist_id = :target_artist_id)....
Find users who listened to similar artists but not target: SELECT u.user_id FROM user_listens u JOIN artist_fans a ON u.artist_id = a.artist_id WHERE a.artist_id = :target_artist_id AND u.user_id NOT IN (SELECT user_id FROM user_listens WHERE artist_id = :target_artist_id). Why: Affinity-based recommendation. Collaborative filtering uses co-listening; this is simpler. Scalability: NOT IN can be slow; use NOT EXISTS or anti-join.
Red Flag: NOT IN with subquery returning nulls—broken semantics. Pro-Move: 'We use NOT EXISTS; scale with approximate similarity (LSH).'
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