Start by clarifying the metric (total order value or count) and the table schema, then outline a SQL solution using aggregation and window functions. Use a subquery to compute per-customer totals per year, then rank customers within each year and filter for the top rank. Mention handling ties and edge cases.
Pro tip: Demonstrate awareness of ties by using RANK() or DENSE_RANK() instead of ROW_NUMBER(), and discuss how to handle multiple top customers if needed. Also, mention that in a real interview, you'd validate assumptions about the data (e.g., date formats, nulls) before writing the query.
Ask whether 'top' means by total order value or count, and confirm the table structure (e.g., columns like customer_id, order_date, order_amount).
Write a subquery to sum order amounts or count orders for each customer, grouped by customer and year (extracted from order_date).
Use a window function like RANK() or DENSE_RANK() over (partition by year order by total desc) to assign ranks.
Select rows where rank = 1, and decide whether to return all tied top customers or just one (e.g., using ROW_NUMBER() if a single customer is required).
Mention potential issues like nulls, date formats, or years with no orders, and how the query would handle them.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.