1000. Find duplicate customer emails — critical scenario 1

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

Solve this production-style DBMS problem. The answer should be safe against duplicates, NULL edge cases or accidental broad updates/deletes where relevant.

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Answer & Explanation

4 Answers

Verified

Option A

Use SELECT * with a CROSS JOIN and no predicate.

Additional Explanation

This option is incorrect for the stated requirement.

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Option B

Ignore duplicate rows and NULL semantics.

Additional Explanation

This option is incorrect for the stated requirement.

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Option C

Run an unqualified UPDATE/DELETE against the entire table.

Additional Explanation

This option is incorrect for the stated requirement.

Verified Correct Answer

Option D

SELECT email,COUNT(*) AS cnt FROM customers WHERE email IS NOT NULL GROUP BY email HAVING COUNT(*)>1;

Additional Explanation

Correct implementation. Prefer parameterized queries in application code, validate affected rows for UPDATE/DELETE, and use transactions for related writes.