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Update customer-placing-the-largest-number-of-orders.sql #13

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Update customer-placing-the-largest-number-of-orders.sql #13

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13 changes: 12 additions & 1 deletion ...er-placing-the-largest-number-of-orders/customer-placing-the-largest-number-of-orders.sql
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Expand Up @@ -9,4 +9,15 @@ LIMIT 1

-- Why are subqueries bad? They're good for readability and often for interviewing. However, in real life subqueries increase the amount of scans taken from the original tables.
-- From a performance tuning perspective, it's often a good idea to reduce the number of subqueries firing every second on the backend.
-- For interviews, it's often a good idea to go with the subquery.
-- For interviews, it's often a good idea to go with the subquery.

WITH RankedCustomers AS (
SELECT
customer_number,
DENSE_RANK() OVER (ORDER BY COUNT(*) DESC) AS rank
FROM Orders
GROUP BY customer_number
)
SELECT customer_number
FROM RankedCustomers
WHERE rank = 1;