SQL COUNT乘以連接表中的條目

Question

我需要知道是否有更好的方法來運行以下查詢。它正在返回錯誤的COUNT號碼，因爲要獲取客戶的地址，我必須加入customers_addresses表，並且某些客戶擁有多個地址。因此，COUNT正乘以用戶擁有的地址數量。我不希望它這樣做，但我仍然想獲取地址信息。有誰知道我該怎麼做？

SELECT 
    Customers.UserID, 
    Customers.FirstName, 
    Customers.LastName, 
    Customers_Addresses.Address1, 
    Customers_Addresses.City, 
    Customers_Addresses.Region, 
    TotalOrders 
FROM 
    (SELECT 
     Customers.UserID, 
     Customers.FirstName, 
     Customers.LastName, 
     Customers_Addresses.Address1, 
     Customers_Addresses.City, 
     Customers_Addresses.Region, 
     Customers.GroupID, 
     COUNT(Orders.OrderID) AS TotalOrders, 
     SUM(Orders.TotalCost) AS TotalSalesOfAllTime 
    FROM 
     Orders 
     INNER JOIN Customers ON Customers.UserID = Orders.UserID 
     INNER JOIN Groups ON Customers.GroupID = Groups.GroupID 
     INNER JOIN Customers_Addresses ON Customers.UserID = Customers_Addresses.UserID 
    GROUP BY Orders.UserID 
) Customers 
INNER JOIN Customers_Addresses ON Customers.UserID = Customers_Addresses.UserID 
WHERE 
    1 = 1 
     AND Customers.UserID BETWEEN 2570 AND 2570 

Answer 1

您可以從內部查詢刪除Customers_Addressses表，因爲你可以在你的主查詢外JOIN它，你在做什麼，反正所以有它的子查詢superflous。

SELECT 
Customers.UserID, 
Customers.FirstName, 
Customers.LastName, 
Customers_Addresses.Address1, 
Customers_Addresses.City, 
Customers_Addresses.Region, 
TotalOrders 
FROM 
(SELECT 
    Customers.UserID, 
    Customers.FirstName, 
    Customers.LastName, 
    Customers.GroupID, 
    COUNT(Orders.OrderID) AS TotalOrders, 
    SUM(Orders.TotalCost) AS TotalSalesOfAllTime 
FROM 
    Orders 
    INNER JOIN Customers ON Customers.UserID = Orders.UserID 
    INNER JOIN Groups ON Customers.GroupID = Groups.GroupID 
GROUP BY Orders.UserID 
) Customers 
INNER JOIN Customers_Addresses ON Customers.UserID = Customers_Addresses.UserID 
WHERE Customers.UserID BETWEEN 2570 AND 2570