3050. Deduplication: Keep the newest customer row for each email and identify older duplicates. — Multi-language REST API

DBMS Published 30 Sept 2026 Updated 30 Sept 2026 0 Views Verified

In a deduplication module, solve this as a production problem using Multi-language REST API: Keep the newest customer row for each email and identify older duplicates. Provide the SQL, explain the logic, show safe application integration, and mention failure/edge cases.

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Answer & Explanation

4 Answers

Verified Correct Answer

Option A

SELECT * FROM (SELECT c.*,ROW_NUMBER() OVER(PARTITION BY email ORDER BY updated_at DESC,id DESC) rn FROM customers c WHERE email IS NOT NULL) x WHERE rn>1;

Additional Explanation

ROW_NUMBER provides a deterministic duplicate ranking. Review rows before deleting them.

Verified

Option B

SELECT * FROM table_name;

Additional Explanation

Incorrect: it does not satisfy the stated business rule and can return/change unintended data.

Verified

Option C

DELETE FROM table_name;

Additional Explanation

Incorrect: it does not satisfy the stated business rule and can return/change unintended data.

Verified

Option D

UPDATE table_name SET status='active';

Additional Explanation

Incorrect: it does not satisfy the stated business rule and can return/change unintended data.