2

我有三个表产品、属性和 product_properties。下面给出了表结构和值的子集：

products
---------------------------------------------
|  id  |  name  |   description   |  price  |
---------------------------------------------
|   1  | Camera |  Color Camera   |   100   |
|   2  | Lens 1 |  Camera Lens 1  |   20    |
|   3  | Lens 2 |  Camera Lens 2  |   30    |
---------------------------------------------

properties
------------------------------------------
|  id |  name          |  display        |
------------------------------------------
|  1  |  lens_mount    |   Lens Mount    |
|  2  |  image_circle  |   Image Circle  |
|  3  |  focal_length  |   Focal Length  |
|  4  |  lens_family   |   Lens Family   |
------------------------------------------

product_properties
------------------------------------------------
|  id  | value    | product_id |  property_id  |
------------------------------------------------
|  1   | F-Mount  | 2          |  1            |
|  2   | C-Mount  | 3          |  1            |
|  3   | 42.01 mm | 2          |  2            |
|  4   | 13.00 mm | 3          |  2            |
|  5   | 10.00    | 2          |  3            |
|  6   | 12.00    | 3          |  3            |
|  7   | Standard | 1          |  4            |
|  8   | Standard | 2          |  4            |
|  9   | Standard | 3          |  4            |
------------------------------------------------

这是我的输出条件：

找到相机 1 的所有镜头（按 lens_family 匹配相机和镜头，这里是“标准”），其中 lens_mount = 'F-Mount' 和 image_circle >= 40 mm 和 focus_length > 5

我为此尝试了以下查询：

SELECT * FROM products 
  INNER JOIN product_properties ON products.id = product_properties.product_id
  INNER JOIN properties ON properties.id = product_properties.property_id 
  WHERE (product_properties.value = 'Standard') 
    AND (properties.name = 'lens_mount' AND product_properties.value = 'F-Mount') 
    AND (properties.name = 'image_circle' AND product_properties.value >= ABS('40 mm')) 
    AND (properties.name = 'focal_length' AND product_properties.value >= 5)

但是，如果只有一个条件，此查询只会给出正确的结果。在所有条件下，它没有任何价值。我尝试在 where 条件下使用 OR 代替 AND，但这也无助于获得正确的输出。

任何人都可以解决这个问题。提前致谢。

4

3 回答 3

3

您想在having子句中而不是在where子句中执行逻辑：

SELECT products.id
FROM products 
  INNER JOIN product_properties ON products.id = product_properties.product_id
  INNER JOIN properties ON properties.id = product_properties.property_id 
group by products.id
having sum(properties.name = 'lens_family' AND product_properties.value = 'Standard') > 0 and
       sum(properties.name = 'lens_mount' AND product_properties.value = 'F-Mount') > 0 and
       sum(properties.name = 'image_circle' AND product_properties.value >= ABS('40 mm')) > 0 and
       sum(properties.name = 'focal_length' AND product_properties.value >= 5) > 0;

您正在寻找单个产品的一组属性。没有一行可以匹配所有条件——它们相互冲突。相反，使用该group by子句将给定产品的行组合在一起。然后计算匹配每个条件的行数。

中的每个子句都having对应于语句中的一个原始子句，由 .where括起来sum()。这会计算匹配的行数。这些条件确保每个属性至少有一行。

于 2013-08-22T20:01:08.533 回答
0

啊，可怕的 EVA 模式。您应该做的第一个想法是根据以下 SQL 创建一个视图来规范化数据。

然后，您可以使用该视图的两个副本（一个用于相机，一个用于镜头）并将它们连接在一起以获得您需要的东西。

SELECT  p.id
        ,p.name
        ,pp1.value as Lens_Mount
        ,pp2.value as Image_Circle
        ,pp3.value as Focal_Length
        ,pp4.value as Lens_Family
from    products p
left outer join
        product_properties pp1
on      pp1.product_id = p.id
and     pp1.property_id = 1 --lens Mount
left outer join
        product_properties pp2
on      pp2.product_id = p.id
and     pp2.property_id = 2 --Image Circle
left outer join
        product_properties pp3
on      pp3.product_id = p.id
and     pp3.property_id = 3 --Focal Length
left outer join
        product_properties pp4
on      pp4.product_id = p.id
and     pp4.property_id = 3 --Lens Family        
where   p.name like 'Lens%'
于 2013-08-22T20:08:27.217 回答
0

您应该对每个条件进行 OR，并计算每个 product_id 满足了多少条件。因此，您使用子句GROUP BY product_id过滤结果。HAVING

SELECT product_properties.product_id, count(*) as conditions_satisfied FROM products 
  INNER JOIN product_properties ON products.id = product_properties.product_id
  INNER JOIN properties ON properties.id = product_properties.property_id 
WHERE product_properties.value = 'Standard'
 OR properties.name = 'lens_mount' AND product_properties.value = 'F-Mount'
 OR properties.name = 'image_circle' AND product_properties.value >= ABS('40 mm')
 OR properties.name = 'focal_length' AND product_properties.value >= 5
GROUP BY product_properties.product_id
HAVING COUNT(*) = 4

请注意，如果您确实需要数字比较，则可能难以比较字符串的属性值。

于 2013-08-22T20:35:58.673 回答