hard20 pts · first answer countssqlwindow-functionsdata-quality

Latest order changes between runs

You pick each customer's latest order with ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY order_date DESC) and keep rn = 1. Some customers show a different order each time the report runs. Why?

A.ROW_NUMBER is random by designB.Those customers have several orders on the same date, so the order of tied rows is not defined; add a tie-breaker such as order_id DESCC.PARTITION BY must come after ORDER BYD.The query cache is corrupt

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