Question

我有三张桌子：

Customer(IdCustomer, Name)
Product(IdProduct, Product)
Order(IdProduct, IdCustomer, nbOrders)

因此订单表存储了客户订购产品的次数。

我需要这样的观点：

TopOrder(Name, Product, nbCommands)

但我只想为每位顾客提供10种产品，他订购的产品最多，我无法弄明白。

Answer 1

dense_rank窗口功能应该是医生规定的：

CREATE View TopOrder AS
SELECT Name, Product, nbOrders
FROM   (SELECT Name, Product, nbOrders,
               DENSE_RANK() OVER (PARTITION BY o.idCustomer
                                  ORDER BY nbOrders DESC) AS rk
        FROM   Customer c
        JOIN   Orders o ON c.idCustomer = o.idCustomer
        JOIN   Product p ON p.idProduct = o.idProduct
       ) t
WHERE  rk <= 10

获取每组的前10行

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