如何在此查询中运行GROUP BY子句？

Question

Write a SELECT statement that returns three columns:

EmailAddress , OrderID , and the order total for each customer .

To do this, you can group the result set by the EmailAddress and OrderID columns.

In addition, you must calculate the order total from the columns in the OrderItems table.

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

You are looking for GROUP BY and 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;

Answer 2

Column must appear in the GROUP BY clause or be used in an aggregate function. Your column

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

does not satisfy this requirement. I assume what you want to do is

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

?