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How do you remove duplicates with partitioning?

SQLmedium0.3 min read

Reviewed by Aditya Kumar · Last reviewed 2026-03-24

**Window + filter**: SELECT * FROM (SELECT *, ROW_NUMBER() OVER (PARTITION BY key_col ORDER BY ts DESC) rn FROM t) t WHERE rn = 1. Keeps latest per key. **Delta Lake**: MERGE with dedup. **OPTIMIZE + Z-order**: Compaction. **Define**: Key columns; ORDER BY for deterministic...

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Frequency
Low
Asked at 1 company
Category
487
questions in SQL
Difficulty Split
130E|271M|86H
in this category
Total Bank
1,863
across 7 categories
Part of the SQL Window Functions Interview Preparation Hub
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Key Concepts Tested
partitionwindow
Expert Answer
52 words

Window + filter: SELECT FROM (SELECT , ROW_NUMBER() OVER (PARTITION BY key_col ORDER BY ts DESC) rn FROM t) t WHERE rn = 1. Keeps latest per key. Delta Lake: MERGE with dedup. OPTIMIZE + Z-order: Compaction. Define: Key columns; ORDER BY for deterministic winner. Scalability: Partition by key for parallelism.

⚡
Pro Tip

Red Flag: Undefined order—non-deterministic dedup. Pro-Move: 'We used ROW_NUMBER ORDER BY event_time DESC, id—deterministic; partitioned by dt for incremental processing.'

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