フリー問題

問題文

A client needs to report the number of distinct customers who bought each product in each store on each day. What is the minimum grain the prepared table must keep?

選択肢

1. One row per customer and day, because distinct customers can be derived by filtering product and store.
2. One row per customer, product, store, and day, because distinct customers cannot be recovered from a total aggregated in advance.
3. One row per product, store, and day, because distinct customers can be derived by summing the daily counts.
4. One row per store and month, because distinct customers can be derived by dividing the monthly totals.