717. Conditional aggregation — edge case 2

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

Write a MySQL query that handles NULL correctly. Avoid accidental three-valued-logic bugs.

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Answer & Explanation

4 Answers

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Option A

Use column = NULL.

Additional Explanation

This option is incorrect for the stated requirement.

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Option B

SELECT SUM(CASE WHEN status='completed' THEN 1 ELSE 0 END) AS completed_count FROM orders;

Additional Explanation

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

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Option C

Use COUNT(column) when you need to count NULL values too.

Additional Explanation

This option is incorrect for the stated requirement.

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Option D

Use NOT IN without considering NULLs in the subquery.

Additional Explanation

This option is incorrect for the stated requirement.