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How do you find duplicates in a table based on one or two columns?

SQLmedium0.3 min readPremium

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62 wordsInterview-ready

**Single column**: SELECT col, COUNT(*) FROM t GROUP BY col HAVING COUNT(*) > 1. **Two columns**: GROUP BY col1, col2 HAVING COUNT(*) > 1. **Full rows**: SELECT * FROM t WHERE (col1, col2) IN (SELECT col1, col2 FROM t GROUP BY col1, col2 HAVING COUNT(*)>1). **Dedup strategy**: ROW_NUMBER() OVER (PARTITION BY key ORDER BY ts DESC) to keep first/last....

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