Interview › Top N per group

SQL interview: top 3 orders per customer (ROW_NUMBER)

“Top 3 per country” is the same pattern as “top 3 per customer.” Number the rows, then keep 1..3.

Prompt. Find the three highest-value orders for each customer. Include ties only if you meant RANK.

Hint: ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY total_amount DESC)

Your T-SQL

SELECT *
FROM (
  SELECT o.*,
         ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY total_amount DESC, order_id DESC) AS rn
  FROM Orders o
) x
WHERE rn <= 3;

RANK keeps ties and can return more than 3. ROW_NUMBER always returns 3. Ask which they wanted.

Then write it on a ticket

Monday is free. A colleague asks, you type, we mark it.

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