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How would you identify duplicate records based on a composite key in SQL?

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To identify duplicates by composite key in SQL, use GROUP BY with HAVING COUNT(*) > 1, or window functions. Example: SELECT order_id, product_id, COUNT(*) cnt FROM orders GROUP BY order_id, product_id HAVING COUNT(*) > 1. Window approach: SELECT * FROM (SELECT *, ROW_NUMBER() OVER (PARTITION BY order_id, product_id ORDER BY created_at) rn FROM orders) t WHERE rn > 1. The GROUP BY method returns only the composite key and count; the window method returns full rows of duplicates....

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