如何在此查詢中運行GROUP BY子句？

Question

編寫返回三列的SELECT語句：

EmailAddress，OrderID和order total每個customer。

爲此，您可以將結果集按EmailAddress和OrderID列分組。

此外，您必須從OrderItems表中的列中計算訂單總額。

SELECT c.EmailAddress, oi.OrderID, (oi.ItemPrice * oi.Quantity) - 
oi.DiscountAmount 
FROM Customers c JOIN Orders o ON c.CustomerID = o.CustomerID 
       JOIN OrderItems oi ON o.OrderID = oi.OrderID 
GROUP BY c.EmailAddress, oi.OrderID 

Answer 1

列必須出現在GROUP BY子句中或用於聚合函數中。您的列

(oi.ItemPrice * oi.Quantity) - oi.DiscountAmount 

不符合此要求。我假設你想要做的是

sum((oi.ItemPrice * oi.Quantity) - oi.DiscountAmount) 

？

Answer 2

您正在尋找GROUP BY和SUM()：

SELECT c.EmailAddress, oi.OrderID, 
     SUM(oi.ItemPrice * oi.Quantity - oi.DiscountAmount) 
FROM Customers c JOIN 
    Orders o 
    ON c.CustomerID = o.CustomerID JOIN 
    OrderItems oi 
    ON o.OrderID = oi.OrderID 
GROUP BY c.EmailAddress, oi.OrderID;