Practice — SQL for Data Analysis (6 questions)

An analyst reports total revenue per country using the schema from the subject (users, events, orders):

SELECT u.country, SUM(o.amount) AS revenue, COUNT(e.event_id) AS events
FROM users  u
JOIN orders o ON o.user_id = u.user_id
JOIN events e ON e.user_id = u.user_id
WHERE o.status = 'paid'
GROUP BY u.country;

Finance says the total revenue is roughly 4× the number in the payments dashboard.

1. Explain precisely why the revenue is inflated, using a small concrete example (one user, a few orders, a few events).
2. Rewrite the query so that both revenue and events are correct, and so that countries whose users have orders but no events still appear.
3. What quick sanity check would have caught this before the report was sent?