Question

我是SQL的初学者，我似乎无法对这个问题提出正确的查询：

使用相关子查询为每个客户返回一行，表示客户最早的订单（具有最早日期的订单）。每行应包括以下三列：EmailAddress，OrderID和OrderDate。

我开始加入订单和客户表。 EmailAddress是customers表中唯一需要的列。

      SELECT EmailAddress, OrderDate, orderID
      FROM Customers c JOIN orders o
      ON c.CustomerID = o.CustomerID

Answer 1

一个不那么复杂的答案：

SELECT  EmailAddress, OrderID, OrderDate AS OldestOrder
  FROM  Customers AS C
        JOIN Orders AS O1
            ON C.CustomerID = O1.CustomerID
 WHERE  O1.OrderDate =
            (SELECT MIN(OrderDate)
             FROM Orders AS O2
             WHERE C.CustomerID = O2.CustomerID)

Answer 2

使用ROW_NUMBER()为按OrderDate降序排序的每位客户获取唯一ID。最新日期为RNO=1。现在在外部查询中进行过滤。

SELECT EmailAddress, OrderDate, orderID
FROM
(
   SELECT ROW_NUMBER() OVER(PARTITION BY c.CustomerID ORDER BY OrderDate DESC)RNO,
   EmailAddress, OrderDate, orderID
   FROM Customers c JOIN orders o
   ON c.CustomerID = o.CustomerID
)TAB 
WHERE RNO=1

Answer 3

您仍然可以使用HAVING子句和IN运算符来实现此特定问题的相同结果

代码：

SELECT DISTINCT EmailAddress, OrderID, OrderDate
FROM Customers
    JOIN orders
    ON Customers.CustomerID = Orders.CustomerID
GROUP BY EmailAddress, OrderID, OrderDate
HAVING OrderID IN (1,2,4,5,6,7,8)
ORDER BY EmailAddress ASC;

SQL Server 2012查询混淆

3 个答案: