MySQL内部聚合没有子查询 - 建议的测试数据已更新

Question

我在MySQL销售数据库中有两个表:

订单表:

CREATE TABLE salestest.`orders` (  
`ID` int(11) unsigned NOT NULL auto_increment,  
`OrderDate` datetime NOT NULL,  
`CustomerID` int(11) unsigned NOT NULL,  
PRIMARY KEY (`ID`),  
UNIQUE KEY `ID` (`ID`),  
KEY `OrderDate` (`OrderDate`),  
KEY `CustomerID` (`CustomerID`)  
) ENGINE=InnoDB;  

INSERT INTO salestest.orders VALUES  
( 1, '2012-04-15', 1 ),  
( 2, '2012-05-20', 1 ),  
( 3, '2012-06-30', 1 );  

OrderDetails表:

CREATE TABLE salestest.`OrderDetails` (  
`ID` int(11) unsigned NOT NULL auto_increment,  
`OrderID` int(11) unsigned NOT NULL,  
`ProductID` int(11) unsigned NOT NULL,  
`Price` double NOT NULL default '0',  
PRIMARY KEY  (`ID`),  
UNIQUE KEY `ID` (`ID`),  
KEY `OrderID` (`OrderID`),  
KEY `ProductID` (`ProductID`),  
CONSTRAINT `OrderID_fk` FOREIGN KEY (`OrderID`) REFERENCES `orders` (`ID`)  
) ENGINE=InnoDB;  

INSERT INTO salestest.OrderDetails VALUES  
( 1, 1, 1, 2 ),  
( 2, 1, 2, 15 ),  
( 3, 1, 3, 22 ),  
( 4, 2, 1, 3 ),  
( 5, 2, 2, 17 ),  
( 6, 2, 3, 23 ),  
( 7, 2, 4, 40 ),  
( 8, 3, 1, 4 ),  
( 9, 3, 2, 20 );  

现在我需要为每个客户选择他们购买每个产品的最后价格.

简单的方法是使用子查询:

SELECT od2.CustomerID,od2.ProductID, od2.Price AS LastPrice, od2.OrderDate AS LastDate  
FROM (SELECT o1.ID, o1.CustomerID, o1.OrderDate, od1.ProductID, od1.Price  
  FROM orders AS o1  
  LEFT JOIN OrderDetails as od1 ON o1.ID=od1.OrderID  
  ORDER BY OrderDate DESC) AS od2  
GROUP BY CustomerID, ProductID  
ORDER BY CustomerID, ProductID;  

结果:

CustomerID ProductID LastPrice LastDate
1 1 4 2012-06-30 00:00:00
1 2 20 2012-06-30 00:00:00
1 3 23 2012-05-20 00:00:00
1 4 40 2012-05- 20 00:00:00

现在的问题; 如果我想避免子查询,临时表或视图,我怎么可能得到相同的结果,我只想使用连接; 此查询是更大查询的一小部分,并且具有子查询的效率非常低.

我试过这个查询:

SELECT o1.CustomerID,od1.ProductID,od1.Price AS LastPrice,o1.OrderDate AS LastDate
FROM Orders AS o1 LEFT JOIN OrderDetails as od1 ON o1.ID = od1.OrderID
GROUP BY CustomerID,ProductID
ORDER BY CustomerID,ProductID;

但它给出了不同的结果:

CustomerID ProductID LastPrice LastDate
1 1 2 2012-04-15 00:00:00
1 2 15 2012-04-15 00:00:00
1 3 22 2012-04-15 00:00:00
1 4 40 2012-05- 20 00:00:00

如您所见,LastPrice和LastDate不正确.我也试过艾伦的建议,但结果是:

CustomerID ProductID LastPrice LastDate
1 1 4 2012-06-30 00:00:00
1 2 20 2012-06-30 00:00:00

首先查询来自spencer的答案结果重复产品:

客户ID产品ID LastPrice LastDate
1 3 22 2012-04-15 00:00:00
1 3 23 2012-05-20 00:00:00
1 4 40 2012-05-20 00:00:00
1 1 4 2012-06- 30 00:00:00
1 2 20 2012-06-30 00:00:00

其他答案都使用子查询,我试图避免.
有什么建议？

Answer 1

更新：

我无法仅使用联接来重现结果集（不使用内联视图或相关子查询）。

我认为不使用内联视图或相关子查询就不可能可靠地返回指定的结果集。

这将返回指定的结果，但没有内联视图，也没有子查询。（但这并不是说这将是返回结果集的“最快”查询。

不工作...请等待

SELECT o1.CustomerID, d1.ProductID, d1.Price, o1.Orderdate
  FROM orders o1
  JOIN OrderDetails d1 ON d1.OrderID = o1.ID
  LEFT      
  JOIN orders o2 
    ON o1.CustomerID = o2.CustomerID
       AND o1.ID <> o2.ID
       AND (o1.OrderDate < o2.OrderDate
           OR (o1.OrderDate = o2.OrderDate AND o1.ID < o2.ID)
           )
  LEFT
  JOIN OrderDetails d2
    ON d2.OrderID = o2.ID
       AND d2.ProductID = d1.ProductId
       AND (o1.OrderDate < o2.OrderDate
           OR (o1.OrderDate = o2.OrderDate AND o1.ID < o2.ID)
           OR (o1.OrderDate = o2.OrderDate AND o1.ID = o2.ID AND d1.ID < d2.ID )
           )
 WHERE d2.ID IS NULL 

此查询将表自身连接起来，并筛选出每个组的“最上面”行。

--

从概念上讲，该查询与以下查询相同。以下查询使用“内联视图”（别名为a和b）。内联视图的目的实际上只是获取与每个 OrderDetail 行关联的 CustomerID 和 OrderDate。

 SELECT a.CustomerID, a.ProductID, a.Price, a.Orderdate
   FROM (SELECT o1.CustomerID, d1.ProductID, d1.Price, o1.OrderDate, d1.OrderID, d1.ID
           FROM orders o1
           JOIN OrderDetails d1 ON d1.OrderID = o1.ID
        ) a
   LEFT      
   JOIN (SELECT o2.CustomerID, d2.ProductID, d2.Price, o2.OrderDate, d2.OrderID, d2.ID
           FROM orders o2
           JOIN OrderDetails d2 ON d2.OrderID = o2.ID
        ) b
     ON a.CustomerID = b.CustomerID
        AND a.ProductID = b.ProductId
        AND a.OrderID <> b.OrderID
        AND a.ID <> b.ID
        AND (a.OrderDate < b.OrderDate 
             OR (a.OrderDate = b.OrderDate AND a.OrderID < b.OrderID)
             OR (a.OrderDate = b.OrderDate AND a.OrderID = b.OrderID AND a.ID < b.ID))
  WHERE b.ID IS NULL 

如果 MySQL 支持的话，我们会使用公共表表达式 (CTE) 来代替内联视图。

最后，这是一种完全不同的方法，它使用 MySQL“用户变量”来模拟 MySQL 中缺少的分析功能。

SELECT q.CustomerID
     , q.ProductID
     , q.Price
     , q.OrderDate
  FROM (SELECT IF(p.CustomerID = @last_customerid,IF(p.ProductID = @last_productid,0,1),1) AS break
             , @last_customerid := p.CustomerID AS CustomerID
             , @last_productid := p.ProductID AS ProductID
             , p.Price
             , p.OrderDate
         FROM (SELECT @last_customerid := NULL, @last_productid := NULL) i
         JOIN ( SELECT o.CustomerID, d.ProductID, o.OrderDate, d.Price 
                  FROM orders o
                  JOIN OrderDetails d ON d.OrderID = o.ID
                 ORDER BY o.CustomerID, d.ProductID, o.OrderDate DESC
              ) p
       ) q
  WHERE q.break = 1