Question

我目前正在https://www.w3schools.com/sql/trysql.asp?filename=trysql_select_all使用数据集来学习SQL。

我给出的问题是“生成所有客户的列表以及他们所拥有的订单的总成本 - 尝试使用round（）函数将总成本显示为2位小数。”

我正在输入代码：

SELECT c.CustomerName, ROUND(sum(CostPerCustomer),2) as "TotalCost"
FROM (
    SELECT c.CustomerName, p.ProductName, (p.Price)*count(c.CustomerName)) AS "CostPerCustomer"
    FROM Customers c, Products p, Orders o, OrderDetails od
    WHERE c.CustomerID = o.CustomerID and p.ProductID = od.ProductID and o.OrderID = od.OrderID
    GROUP BY c.CustomerName, p.ProductName
    ORDER BY c.CustomerName, count(c.CustomerName) desc)
GROUP BY CustomerName

我收到错误消息'您试图执行不包含指定表达式'p.Price * count（c.CustomerName）'的查询作为聚合函数的一部分。'

是否有人能够告诉我我的代码有什么问题以及我如何修复它？

Answer 1

你可以试试这个

    SELECT CustomerName, round(sum(price*Quantity),2) AS TotalCost   FROM Customers C
    JOIN Orders O ON C.CustomerID = O.CustomerID
    JOIN OrderDetails OD ON O.OrderID = OD.OrderID
    JOIN Products P ON P.ProductID = OD.ProductID
    GROUP BY CustomerName;

Answer 2

这是一个如何连接多个表并解决问题的示例。 count（c.CustomerName）在这里不正确，你必须去订单表并获得属于客户的所有orderid，然后你去orderdetails表找到他们订购的产品和数量。然后，您转到产品表并获取每种产品的价格。

select c.customerid,c.customername,sum(p.price*od.quantity)
from customers c
join orders o on o.customerid=c.customerid
join orderdetails od on od.orderid=o.orderid
join products p on p.productid=od.productid
group by c.customerid,c.customername
order by c.customerid

Answer 3

让我先纠正您当前的查询，使用适当的明确JOIN s（即INNER JOIN）

SELECT  
        c.CustomerName, ROUND(SUM(p.Price * od.Qty), 2) AS "TotalCostPerCustomer"
FROM Customers c
INNER JOIN Orders o ON c.CustomerID = o.CustomerID
INNER JOIN OrderDetails od ON o.OrderID = od.OrderID
INNER JOIN Products p ON p.ProductID = od.ProductID
GROUP BY c.CustomerName

SQL - 您尝试执行不包含指定表达式作为聚合函数一部分的查询

3 个答案: