SQL 查询用于计算每个客户的订单数量和总金额

Question

我有两个 Order带有列的表：

OrderID,OrderDate,CID,EmployeeID

并OrderItem带有列：

OrderID,ItemID,Quantity,SalePrice

我需要返回客户 ID(CID)、每个客户的订单数以及每个客户所有订单的总金额。

到目前为止，我有两个单独的查询。其中一个给我客户订单的数量......

SELECT CID, Count(Order.OrderID) AS TotalOrders
FROM [Order]
Where CID = CID 
GROUP BY CID
Order BY Count(Order.OrderID) DESC;

另一个给我总销售额。我在组合它们时遇到了麻烦......

SELECT CID, Sum(OrderItem.Quantity*OrderItem.SalePrice) AS TotalDollarAmount
FROM OrderItem, [Order]
WHERE OrderItem.OrderID = [Order].OrderID
GROUP BY CID

我在 Access 2010 中执行此操作。

Answer 1

COUNT(DISTINCT ...)您可以在其他 SQL 引擎中使用：

SELECT CID, 
       Count(DISTINCT O.OrderID) AS TotalOrders, 
       Sum(OI.Quantity*OI.SalePrice) AS TotalDollarAmount 
FROM [Order] O
INNER JOIN [OrderItem] OI
  ON O.OrderID = OI.OrderID
GROUP BY CID 
Order BY Count(DISTINCT O.OrderID) DESC

遗憾的是 Access 不支持。相反，您可以先获取订单美元金额，然后在计算订单数之前将它们合并：

SELECT CID,
       COUNT(Orders.OrderID) AS TotalOrders,
       SUM(OrderAmounts.DollarAmount) AS TotalDollarAmount
FROM [Orders]
INNER JOIN (SELECT OrderID, Sum(Quantity*SalePrice) AS DollarAmount 
      FROM OrderItems GROUP BY OrderID) AS OrderAmounts
  ON Orders.OrderID = OrderAmounts.OrderID
GROUP BY CID
ORDER BY Count(Orders.OrderID) DESC

如果您需要包括订单不含商品的客户（不常见但可能），请更改INNER JOIN为LEFT OUTER JOIN。