MySQL - 使用子查詢來查找平均值

我遇到此查詢的語法問題。我試圖從各個國家返回一家公司的最大總額。MySQL - 使用子查詢來查找平均值

的表格看起來像：

Orders 
Columns 
    OrderID 
    CustomerID 
    EmployeeID 
    OrderDate 
    RequiredDate 

OrderDetails 
Columns 
    OrderID 
    ProductID 
    UnitPrice 
    Quantity 

Products 
Columns 
    ProductID 
    ProductName 
    QuantityPerUnit 
    UnitPrice 

Customers 
Columns 
    CustomerID 
    CompanyName 
    ContactName 
    Country

我曾嘗試以下：

SELECT 
    T1.Country, 
    CompanyName, 
    T1.OrderSum 
FROM 
    (SELECT 
     C.Country, 
     C.CompanyName, 
     SUM(UnitPrice * Quantity) AS OrderSum 
    FROM Customers C 
     JOIN Orders O 
      ON C.CustomerID = O.CustomerID 
     JOIN OrderDetails D 
      ON D.OrderID = O.OrderID 
    GROUP BY C.Country) T1 
      JOIN 
      -- TOP PAYMENT TOTALS BY COUNTRY 
      (SELECT COUNTRY, 
        MAX(OrderSum) AS OrderSum 
      FROM 
      -- PAYMENT TOTALS BY CUSTOMER 
       (SELECT  C.Country, 
          C.CompanyName, 
          SUM(UnitPrice * Quantity) AS OrderSum 
       FROM Customers C 
        JOIN Orders O1 
         ON O1.CustomerID = C.CustomerID 
        JOIN OrderDetails D1 
         ON D1.OrderID = O1.OrderID 
       GROUP BY C.COUNTRY, C.CompanyName) T2 
      GROUP BY COUNTRY) T3 
     ON T1.COUNTRY = T3.COUNTRY 
      AND T1.OrderSum = T3.OrderSum 
ORDER BY Country;

此查詢僅返回三個國家：

Ireland Hungry Owl All-Night Grocers 57317.3900 
Norway Sant Gourmet 5735.1500 
Poland Wolski Zajazd 3531.9500

但是，這個查詢我試過了，返回所有國家，但我不確定它是否正確，因爲我沒有像在pre中那樣包含'max'值vious查詢：

SELECT 
    T1.Country, 
    CompanyName, 
    T1.OrderSum 
FROM 
    (SELECT 
     C.Country, 
     C.CompanyName, 
     SUM(UnitPrice * Quantity) AS OrderSum 
    FROM Customers C 
     JOIN Orders O 
      ON C.CustomerID = O.CustomerID 
     JOIN OrderDetails D 
      ON D.OrderID = O.OrderID 
    GROUP BY C.CompanyName) T1 
GROUP By Country 
ORDER BY Country;

我也不能確定，如果我正確地計算訂單總數，這可能是我的一部分錯誤。但我試圖從每個訂單數量最多的國家找到公司。對不起，所有的文字。

來源

2017-04-07 Babeeshka

下面的查詢將只列出每個國家最大的訂單總額的公司：

SELECT A.Country, A.CompanyName, A.OrderSum 
FROM (
    SELECT 
     C.Country, 
     C.CompanyName, 
     SUM(D.UnitPrice * D.Quantity) AS OrderSum 
    FROM Customers C 
     JOIN Orders O ON C.CustomerID = O.CustomerID 
     JOIN OrderDetails D ON D.OrderID = O.OrderID 
    GROUP BY 
     C.Country, C.CustomerID 
) A 
JOIN (
    SELECT 
     S.Country, MAX(S.OrderSum) as MaxSum 
    FROM (
     SELECT 
      C.Country, 
      C.CompanyName, 
      SUM(D.UnitPrice * D.Quantity) AS OrderSum 
     FROM Customers C 
      JOIN Orders O ON C.CustomerID = O.CustomerID 
      JOIN OrderDetails D ON D.OrderID = O.OrderID 
     GROUP BY 
      C.Country, C.CustomerID 
     ) S 
    GROUP BY 
     S.Country 
) B ON A.Country = B.Country 
WHERE 
    A.Country = B.Country AND 
    A.OrderSum = B.MaxSum 
ORDER BY 
    A.Country, A.CompanyName 
;

[更新]

注意上面的SQL如下OrderSum在您列出的查詢計算方法。鑑於表Products有QuantityPerUnit和UnitPrice，我懷疑你的OrderSum也應該乘以QuantityPerUnit - 在這種情況下，你需要修改數學爲OrderSum。

來源

2017-04-07 20:45:40

MySQL - 使用子查詢來查找平均值

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