通過訂單檢索客戶 - 主題的變體

Created: November-22, 2018

這將獲得所有客戶的所有訂單：

SELECT c.CustomerName, o.OrderID
    FROM Customers AS c
    INNER JOIN Orders AS o
        ON c.CustomerID = o.CustomerID
    ORDER BY c.CustomerName, o.OrderID;

這將計算每個客戶的訂單數量：

SELECT c.CustomerName, COUNT(*) AS 'Order Count'
    FROM Customers AS c
    INNER JOIN Orders AS o
        ON c.CustomerID = o.CustomerID
    GROUP BY c.CustomerID;
    ORDER BY c.CustomerName;

此外，計數，但可能更快：

SELECT  c.CustomerName,
        ( SELECT COUNT(*) FROM Orders WHERE CustomerID = c.CustomerID ) AS 'Order Count'
    FROM Customers AS c
    ORDER BY c.CustomerName;

僅列出訂單的客戶。

SELECT  c.CustomerName,
    FROM Customers AS c
    WHERE EXISTS ( SELECT * FROM Orders WHERE CustomerID = c.CustomerID )
    ORDER BY c.CustomerName;