1725. Delete duplicates safely — Manufacturing — implementation variant 25

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

In a Manufacturing application, implement this production problem: Delete duplicate customers while keeping the smallest ID for each email. The API/service receives user input and must return or modify data safely. Give the SQL solution, explain why it works, and show how the same operation is called from the selected stack.

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Answer & Explanation

4 Answers

Verified

Option A

SELECT * FROM the_table;

Additional Explanation

Incorrect: it does not implement the stated business rule and may modify/fetch the wrong rows.

Verified Correct Answer

Option B

DELETE c1 FROM customers c1 JOIN customers c2 ON c1.email=c2.email AND c1.id>c2.id WHERE c1.email IS NOT NULL;

Additional Explanation

The self-join identifies later duplicate IDs. Preview with SELECT and use a backup/transaction before deletion.

Verified

Option C

DELETE FROM the_table;

Additional Explanation

Incorrect: it does not implement the stated business rule and may modify/fetch the wrong rows.

Verified

Option D

UPDATE the_table SET status='active';

Additional Explanation

Incorrect: it does not implement the stated business rule and may modify/fetch the wrong rows.