59. Each Customer's Most Expensive Order
HardSubqueriesgreatest-n-per-groupcorrelated subqueryMAX
Greatest-n-per-group asks for the top row within each group. A classic approach keeps a row only when no other row in its group beats it — expressed with a correlated subquery.
Task: return each customer's single most expensive order. The data is built so each customer's maximum amount is unique (no ties), giving exactly one row per customer.
Return columns customer, order_id, amount. Order by customer ascending.
Tables
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Expected outputrows must come back in this order
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