注文数が最も多い顧客の合計注文数を返すサブクエリを作成します。customerid と発注数を含めます。
USE Northwind
GO
SELECT CustomerID,
COUNT(Orders.OrderID) AS TotalOrders,
SUM(OrderAmounts.DollarAmount) AS TotalDollarAmount
FROM [Orders]
Left Outer JOIN (SELECT OrderID, Sum(Quantity*SalePrice) AS DollarAmount
FROM OrderItems GROUP BY OrderID) AS OrderAmounts
ON Orders.OrderID = OrderAmounts.OrderID
GROUP BY CustomerID
ORDER BY Count(Orders.OrderID) DESC
次のような応答が返ってきました: Msg 208, Level 16, State 1, Line 1 無効なオブジェクト名 'OrderItems'。
???