1726. Order totals by customer — E-commerce — implementation variant 26

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

In a E-commerce application, implement this production problem: Calculate completed revenue for every customer, including customers with zero revenue. 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 Correct Answer

Option A

SELECT c.id,c.name,COALESCE(SUM(CASE WHEN o.status='completed' THEN o.total_amount ELSE 0 END),0) revenue FROM customers c LEFT JOIN orders o ON o.customer_id=c.id GROUP BY c.id,c.name;

Additional Explanation

LEFT JOIN keeps zero-order customers; conditional aggregation avoids excluding non-completed orders.

Verified

Option B

UPDATE the_table SET status='active';

Additional Explanation

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

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

SELECT * FROM the_table;

Additional Explanation

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