2393. Messaging: Count unread messages per user. — Python + FastAPI + SQLAlchemy

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

In a messaging module, solve this as a production problem using Python + FastAPI + SQLAlchemy: Count unread messages per user. 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

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 B

SELECT * FROM table_name;

Additional Explanation

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

Verified

Option C

DELETE FROM table_name;

Additional Explanation

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

Verified Correct Answer

Option D

SELECT recipient_id,COUNT(*) unread_count FROM messages WHERE read_at IS NULL GROUP BY recipient_id;

Additional Explanation

IS NULL is required because NULL cannot be compared using =.