635. Union normalized labels — set challenge 2

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

Write a MySQL-compatible set/anti-set query for the requirement. Remember that UNION removes duplicates while UNION ALL preserves them.

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Answer & Explanation

4 Answers

Verified

Option A

Use UPDATE instead of a set operation.

Additional Explanation

This option is incorrect for the stated requirement.

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Option B

Use CROSS JOIN for set difference.

Additional Explanation

This option is incorrect for the stated requirement.

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Option C

Always use UNION ALL even when duplicates must be removed.

Additional Explanation

This option is incorrect for the stated requirement.

Verified Correct Answer

Option D

SELECT 'employee' AS type,id,name FROM employees UNION ALL SELECT 'customer',id,name FROM customers;

Additional Explanation

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