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Removing duplicates - ROW_NUMBER() or DISTINCT

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ROW_NUMBER(): use when you need to pick one row per group (e.g., keep latest). More control than DISTINCT. DISTINCT: removes duplicates across all columns; use when entire row is duplicate. ROW_NUMBER with PARTITION BY key, ORDER BY ts DESC, filter rn=1 gives deterministic dedup. DISTINCT is simpler but doesn't let you choose which duplicate to keep. **Why it matters**: Design choices compound at scale—wrong approach can cause 100× overhead....

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