选择所有属性的一个

Question

搜索时，我有如下表：

表：属性

+---------------+-------------+ 
| attribute_id | name  | 
+---------------+-------------+ 
| 1    | color  | 
| 2    | material | 
+---------------+-------------+ 

表：ATTRIBUTE_VALUES

+---------------------+-----------------+--------------+--------------+ 
| attribute_value_id | attribute_id | product_id | value  | 
+---------------------+-----------------+--------------+--------------+ 
| 1     | 1    | 1   | blue   | 
| 2     | 2    | 1   | metal  | 
| 3     | 1    | 2   | red   | 
| 4     | 2    | 2   | metal  | 
+---------------------+-----------------+--------------+--------------+ 

和我有以下查询：

SELECT 
       p.product_id    AS product_id, 
       p.name      AS product_name, 
       v.value      AS attribute_value, 
       a.attribute_id    AS attribute_id, 
       a.attribute_category_id  AS attribute_category_id, 
       a.name      AS attribute_name, 
       c.name      AS attributes_category_name 
    FROM 
       products p 
    LEFT JOIN 
       attribute_values v USING (product_id) 
    LEFT JOIN 
       attributes a USING (attribute_id) 
    LEFT JOIN 
       attribute_categories c USING (attribute_category_id) 
    WHERE 
       (a.name = 'color' AND v.value = 'red') 

该查询的问题是：当产品匹配WHERE-clausule时，我需要所有属性。

所以我得到是这样的：我只得到'颜色'属性，但正如你所看到的，具体的产品也有'材料'属性。

所以，当我搜索红色的产品时，我还想要该特定产品的其他属性（材质=金属）。

Answer 1

这里有一个理念 - 减少到它的本质......

SELECT x.* 
    FROM 
    (SELECT product_id 
      , MAX(CASE WHEN attribute_id = 1 THEN value END) color 
      , MAX(CASE WHEN attribute_id = 2 THEN value END) material 
     FROM attribute_values 
     GROUP 
      BY product_id 
    ) x 
WHERE color = 'red'; 

哦，并注意attribute_value_id似乎起不到任何作用。

Answer 2

我想我找到了答案：

SELECT 
       p.product_id    AS product_id, 
       p.name      AS product_name, 
       v.value      AS attribute_value, 
       a.attribute_id    AS attribute_id, 
       a.attribute_category_id  AS attribute_category_id, 
       a.name      AS attribute_name, 
       c.name      AS attributes_category_name 
    FROM 
       products p 
    LEFT JOIN 
       attribute_values v USING (product_id) 
    LEFT JOIN 
       attributes a USING (attribute_id) 
    LEFT JOIN 
       attribute_categories c USING (attribute_category_id) 
    WHERE 
       p.product_id IN (SELECT p.product_id FROM products p LEFT JOIN attribute_values v USING (product_id) LEFT JOIN attributes a USING (attribute_id) WHERE a.name = 'color' AND v.value = 'red')