Question

我正在寻找一个更优雅的解决方案，解决我在使用与GROUP BY一起使用的MySQL MIN（）时遇到的问题。

我有两张桌子：

产品（id，group_id）
product_attributes（product_id，attribute_id，value）

我希望从某个产品组中选择每个金属组中最便宜的金属（attribute_id = 40）。

以下查询有效，但我确信它写得好得多。

SELECT metal.product_id, metal.value AS `metal`, `price`.value AS `price`
FROM
    product_attributes metal
INNER JOIN
    (
        SELECT metal.value AS `metal`, MIN(price.value) AS `price`
        FROM 
            product_attributes metal
        LEFT JOIN 
            product_attributes price
        ON metal.product_id = price.product_id
        INNER JOIN products p
        ON p.id = metal.product_id
        WHERE
            metal.attribute_id = 40 AND
            price.attribute_id = 37 AND
            p.group_id = 1
        GROUP BY
            metal.value
        ORDER BY metal ASC, price DESC
    ) AS d ON
    d.metal = metal.value
LEFT JOIN
    product_attributes price ON
    metal.product_id = price.product_id AND price.attribute_id = 37
INNER JOIN
    products p ON
    p.id = metal.product_id
WHERE
    metal.attribute_id = 40
    AND d.price = price.value
    AND p.group_id = 1
GROUP BY
    metal.value
ORDER BY
    metal.value ASC,
    price.value DESC;

Answer 1

我认为你可以把它写成group by声明：

  SELECT metal.value AS `metal`, metal.product_id, MIN(price.value) AS `price`
  FROM product_attributes metal LEFT JOIN 
       product_attributes price
       ON metal.product_id = price.product_id
       INNER JOIN products p
       ON p.id = metal.product_id
  WHERE metal.attribute_id = 40 AND
        price.attribute_id = 37 AND
        p.group_id = 1
  GROUP BY metal
  order by metal, price

这是有效的，假设每product_id有一个metal.value。如果有多个此类产品ID，则需要重新加入属性表：

SELECT metal.product_id, metal.value AS `metal`, d.`price`
FROM (SELECT metal.value AS `metal`, MIN(price.value) AS `price`
      FROM product_attributes metal LEFT JOIN 
           product_attributes price
           ON metal.product_id = price.product_id
           INNER JOIN products p
           ON p.id = metal.product_id
      WHERE metal.attribute_id = 40 AND
            price.attribute_id = 37 AND
            p.group_id = 1
      GROUP BY metal
    ) d join
    product_attributes metal
    ON d.metal = metal.value
ORDER BY metal.value ASC, d.price DESC

您可能还需要where和其他联接。这取决于数据的结构。

Answer 2

最终解决方案比我简单。我在内部查询中按价格订购了我的数据，因此在GROUP BY之前强制进行排序，这样我就能得到我所需要的（每个金属组中最便宜的产品）。

SELECT * FROM
            (
                SELECT metal.enum_id AS `metal`, metal.product_id FROM product_attributes metal
                LEFT JOIN product_attributes price ON metal.product_id = price.product_id AND price.attribute_id = 37
                INNER JOIN products p ON p.id = metal.product_id
                WHERE
                    metal.attribute_id = 40 AND
                    p.group_id = 1 AND
                    p.id NOT IN (SELECT DISTINCT product_id FROM product_attributes WHERE (attribute_id=162 OR attribute_id=204 OR attribute_id=205) AND `value`=1)
                ORDER BY price.value+'0' ASC 
            ) AS s
            GROUP BY metal

SQL MIN（）＆amp;通过...分组

2 个答案: