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我有四个 MySQL 表：contacts、orders、ordered_products 和 products，我正在尝试编写一些报告查询。这是其中之一：

SELECT t1.name, t1.contact_id, SUM(t1.prodSoldQty) AS contactSoldQty, SUM(t1.prodSoldVol) AS soldVol
FROM contacts
INNER JOIN
(
 SELECT 
    contacts.name,
        ordered_products.product_id,
        ordered_products.contact_id,
        SUM(ordered_products.quantity) AS prodSoldQty,
        (products.price * SUM(ordered_products.quantity)) AS prodSoldVol
 FROM ordered_products
 INNER JOIN contacts ON contacts.id = ordered_products.contact_id
 INNER JOIN products ON products.id = ordered_products.product_id
 INNER JOIN orders ON orders.id = ordered_products.order_id
 GROUP BY ordered_products.product_id , ordered_products.contact_id
 ORDER BY ordered_products.product_id
) AS t1 ON t1.contact_id = contacts.id
GROUP BY contacts.id
ORDER BY t1.name;

一切都按预期工作，尽管如果我添加（并且我需要添加）另一个 [LEFT|INNER] JOIN（例如：INNER JOIN orders ON orders.contact_id = contacts.id），行 SUM 总数搞砸了（他们似乎根据订单数量重复，三份...）。我想问题可能是第一个连接派生表中的多个分组。然而它却让我望而却步。在这里，您可以找到上述查询的略微变体。即使是这个微小的修改也能够触发“问题”：

SELECT t1.name, t1.contact_id,
SUM(t1.prodSoldQty) AS contactSoldQty,
SUM(t1.prodSoldVol) AS soldVol
FROM contacts
INNER JOIN
(
 SELECT 
    contacts.name,
        ordered_products.product_id,
        ordered_products.contact_id,
        SUM(ordered_products.quantity) AS prodSoldQty,
        (products.price * SUM(ordered_products.quantity)) AS prodSoldVol
 FROM ordered_products
 INNER JOIN contacts ON contacts.id = ordered_products.contact_id
 INNER JOIN products ON products.id = ordered_products.product_id
 INNER JOIN orders ON orders.id = ordered_products.order_id
 GROUP BY ordered_products.product_id , ordered_products.contact_id
 ORDER BY ordered_products.product_id
) AS t1 ON t1.contact_id = contacts.id
INNER JOIN orders ON orders.contact_id = contacts.id
WHERE orders.order_state_id != '111'
GROUP BY contacts.id
ORDER BY t1.name;

上述路径是死胡同。在@Gordon Linoff 的帮助下，我找到了更好的方法。报告目标之一是在客户/联系人基础上计算总产品成本金额和总产品销售金额。我专注于通过两个单独的连接来做到这一点。似乎一个就足够了（避免包括几次几乎相同的表）：

SELECT t1.name, t1.contact_id,
SUM(t1.prodSellQty) AS sellQty,
SUM(t1.prodCostVol) AS costAmount,
SUM(t1.prodSellVol) AS sellAmount
FROM contacts
INNER JOIN
(
 SELECT 
    contacts.name,
        ordered_products.contact_id,
        SUM(ordered_products.quantity) AS prodSellQty,
        SUM(products.price * ordered_products.quantity) AS prodCostVol,
        SUM(ordered_products.price * ordered_products.quantity) AS prodSellVol
 FROM ordered_products
 INNER JOIN contacts ON contacts.id = ordered_products.contact_id
 INNER JOIN products ON products.id = ordered_products.product_id
 INNER JOIN orders ON orders.id = ordered_products.order_id
 GROUP BY ordered_products.product_id , ordered_products.contact_id
 ORDER BY ordered_products.product_id
) AS t1 ON t1.contact_id = contacts.id
GROUP BY contacts.id
ORDER BY contacts.name;

谢谢，卢卡

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