MySQL属性数据库

Question

我有一个属性数据库。每个属性值都存储在一个带有其父属性 ID 的表中。

在一个独立的表中，我会编写一个提取数据的 SQL 语句

WHERE username = '' AND domain = ''  

在属性表中，因为每个值都存储为单独的行，所以我不能这样做。我有一个连接，可以让我带回一个值 + 结果（见下文），但是我需要一个基于2个标准如上图..

SELECT upa.value, up.status, u.status
  FROM user_product up, product_attribute pa, product p, user u, user_product_attribute upa

 WHERE pa.attribute_name = 'username'
   AND pa.product_attribute_id = upa.product_attribute_id
   AND pa.product_id = p.product_id
   AND u.user_id = up.user_id
   AND up.user_product_id = upa.user_product_id

   AND p.product_name = 'email'
   AND upa.value      = 'exampleuser'

我想我需要以某种形式再次加入上述能力？任何输入都会有所帮助..

谢谢

Answer 1

请不要使用隐式连接语法。需要第二组连接才能获得第二个属性。

SELECT upa1.value, upa2.value, up1.status, u1.status 
  FROM product p
    /* These joins get attribute/value for 'username' attribute */
    INNER JOIN product_attribute pa1
      ON p.product_id = pa1.product_id
        AND pa1.attribute_name = 'username'
    INNER JOIN user_product_attribute upa1
      ON pa1.product_attribute_id = upa1.product_attribute_id
    INNER JOIN user_product up1
      ON upa1.user_product_id = up1.user_product_id
    INNER JOIN user u1
      ON up1.user_id = u1.user_id 
    /* These joins get attribute/value for 'domain' attribute */  
    INNER JOIN user_product_attribute upa2 
      ON upa1.user_product_id = upa2.user_product_id
    INNER JOIN product_attribute pa2
      ON upa2.product_attribute_id = pa2.product_attribute_id            
        AND pa2.attribute_name = 'domain'
  WHERE p.product_name = 'email'

Answer 2

您需要将所有连接重复两次才能获得这两个属性。如果您一次需要超过 2 或 3 个属性，这并不漂亮。

SELECT upa.value, up.status, u.status
FROM user_product up
JOIN user u    ON u.user_id = up.user_id

-- Join to get attribute 'username'
JOIN user_product_attribute upa1 ON up.user_product_id = upa1.user_product_id
JOIN product_attribute pa1 ON pa1.product_attribute_id = upa1.product_attribute_id
JOIN product p1                  ON pa1.product_id = p1.product_id

-- Join to get attribute 'domain'    
JOIN user_product_attribute upa2 ON up.user_product_id = upa2.user_product_id
JOIN product_attribute pa2 ON pa2.product_attribute_id = upa2.product_attribute_id
JOIN product p2                  ON pa2.product_id = p2.product_id

WHERE pa1.attribute_name = 'domain'
  AND p1.product_name = 'email'
  AND upa1.value      = 'exampledomain.com'

  AND pa2.attribute_name = 'username'
  AND p2.product_name = 'email'
  AND upa2.value      = 'exampleuser'
;