Write SQL against a sample shop database and run it. PostgreSQL runs here in your browser, so nothing you do reaches a server: insert, update, drop tables, and reset the database whenever you like.
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select c.country, count(*) as orders, sum(oi.quantity * oi.unit_price) as revenue from orders o join customers c on c.customer_id = o.customer_id join order_items oi on oi.order_id = o.order_id where o.status <> 'cancelled' group by c.country order by revenue desc;