3747. Deduplication: Find duplicate phone numbers while ignoring blank values. — Data Migration

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

In a deduplication module, solve this as a production problem using Data Migration: Find duplicate phone numbers while ignoring blank values. Provide the SQL, explain the logic, show safe application integration, and mention failure/edge cases.

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Answer & Explanation

4 Answers

Verified

Option A

SELECT * FROM table_name;

Additional Explanation

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

Verified Correct Answer

Option B

SELECT phone,COUNT(*) cnt FROM customers WHERE phone IS NOT NULL AND TRIM(phone)<>'' GROUP BY phone HAVING COUNT(*)>1;

Additional Explanation

Filtering blank/null values prevents meaningless duplicate groups.

Verified

Option C

UPDATE table_name SET status='active';

Additional Explanation

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

Verified

Option D

DELETE FROM table_name;

Additional Explanation

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