MySQL查询-对一个相关表求和-对另一个相关表进行计数

Question

Count在一个相关的表上工作正常，但是当我添加Sum时，Count中的结果就显得过高了。

SELECT Orders.kp_OrderID AS `Order #`, 
    Orders.t_ServiceLevel AS `Service Level`, 
    Customers.t_CustCompany AS Company, 
    Orders.t_JobName AS `Job Name`, 
    Orders.t_JobStatus AS `Status`, 
    Orders.d_JobDue AS Due, 
    Orders.ti_JobDue AS Time, 
    COUNT(OrderItems.kf_OrderID) AS `Line Item`, 
    SUM(
        `OrderItemComponents`.`n_QuantityPrintMaterial` * (
        `OrderItemComponents`.`n_WidthInInches` * `OrderItemComponents`.`n_HeightInInches` / 144
            )
        ) AS SqFt, 
    Orders.nb_JobFinished AS Finished
FROM Orders 
     INNER JOIN OrderItems ON Orders.kp_OrderID = OrderItems.kf_OrderID
     INNER JOIN Customers ON Orders.kf_CustomerID = Customers.kp_CustomerID
     INNER JOIN OrderItemComponents ON OrderItemComponents.kf_OrderID = Orders.kp_OrderID
    WHERE Orders.d_JobDue > (
        DATE_SUB(CURDATE(), INTERVAL 60 DAY)
         )
    GROUP BY Orders.kp_OrderID
    ORDER BY `Line Item` DESC

Answer 1

将您的COUNT行切换为：

COUNT(DISTINCT OrderItems.kf_OrderID) AS `Line Item`

添加线时

INNER JOIN OrderItemComponents 
  ON OrderItemComponents.kf_OrderID = Orders.kp_OrderID

您返回了更多的行，因为我假设OrderItem可以包含多个组件。

更新

如果您有COUNT条语句，请尝试就地使用它：

(SELECT COUNT(OrderItems.kf_OrderID) 
 FROM OrderItems.kf_OrderID 
 WHERE OrderItems.kf_OrderID=Order.kf_OrderID) AS `Line Item`,

Answer 2

我假设您为每个订单项组件重复了每个订单项。 一种解决方案可能是COUNT(DISTINCT OrderItems.kf_OrderID)因此您不会两次计算同一项目。