Start by clarifying the schema and business definitions (e.g., revenue = quantity * price, city from customer address). Then write a SQL query that joins customers, orders, and order items, groups by city, and sums revenue. Finally, discuss handling edge cases like null cities and performance considerations.
Pro tip: Mention that you'd validate the query against a sample dataset or use a subquery to pre-aggregate revenue per order to avoid fan-out issues. Also, consider adding a comment on how you'd handle cities with no orders (e.g., using LEFT JOIN if needed).
Ask about the tables involved (e.g., customers, orders, order_items) and how revenue is defined (e.g., quantity * unit_price). Confirm that 'city' comes from the customer's address.
Determine the join path: customers to orders (on customer_id), orders to order_items (on order_id). Ensure you use INNER JOINs to only include orders with revenue.
Use SUM(quantity * unit_price) as total_revenue, GROUP BY customer city, and ORDER BY total_revenue DESC for readability. Include customer city in the SELECT.
Discuss handling NULL cities (e.g., COALESCE to 'Unknown'), and mention indexing on join keys and city for performance. Consider pre-aggregating order totals to avoid large intermediate results.
Walk through a sample result, explain how you'd test the query, and mention any assumptions made (e.g., currency, date range).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.