Question

我有许多品牌的产品，用户可以喜欢（多对多），用户也可以关注品牌。对于主页，我需要用户添加到收藏夹的所有产品以及用户跟随的品牌产品。

我已经提供了以下SQL查询，但是它的工作方式并不像预期的那样 - 它只返回来自后续品牌并且在收藏夹中同时出现的产品。

SELECT * FROM products
INNER JOIN favorites ON products.id = favorites.favorable_id
INNER JOIN followings ON products.merchant_id = followings.followable_id
WHERE favorites.favorable_type = 'Product' AND favorites.user_id = ?
AND followings.followable_type = 'Merchant' AND followings.user_id = ?

如何正确修复查询？提前谢谢。

编辑：我将拥有10k +产品，1k +用户。所以我需要最快的执行时间查询。

Answer 1

一种“简单”方法（仅修改现有查询）可能是将INNER JOIN转换为LEFT JOIN并检查at least one of the two joined successfully中的WHERE子句...

SELECT
  *
FROM
  products
LEFT JOIN
  favorites
    ON  products.id = favorites.favorable_id
    AND favorites.favorable_type = 'Product'
    AND favorites.user_id = ?
LEFT JOIN
  followings
    ON  products.merchant_id = followings.followable_id
    AND followings.followable_type = 'Merchant'
    AND followings.user_id = ?
WHERE
      favorites.user_id IS NOT NULL
  OR followings.user_id IS NOT NULL

这样做的缺点是product表中的每条记录都必须由WHERE子句检查。

如果该表很小，或者您通常以任何方式返回表的“大”部分，这可能没问题。但是，如果您只返回表格的“小”部分，则可能需要对此进行优化，例如使用UNION的两个查询，如问题标题所暗示的那样......

SELECT
  products.*
FROM
  products
INNER JOIN
  favorites
    ON  products.id = favorites.favorable_id
    AND favorites.favorable_type = 'Product'
    AND favorites.user_id = ?

UNION

SELECT
  products.*
FROM
  products
INNER JOIN
  followings
    ON  products.merchant_id = followings.followable_id
    AND followings.followable_type = 'Merchant'
    AND followings.user_id = ?

此处的INNER JOIN每个LEFT JOIN可能明显快于基于followings(user_id, followable_type)的整个查询，因为可能会使用favorites(user_id, favorable_type)和{{1}}上的索引。

Answer 2

尝试替换

 INNER JOIN followings ON products.merchant_id = followings.followable_id

与

left JOIN followings ON favorites.favorable_id = followings.followable_id

Answer 3

select p.*
from products as p
where
    exists (
       select *
       from favorites as f
       where f.favorable_id = p.id and f.favorable_type = 'Product' and f.user_id = ?
    ) or
    exists (
       select *
       from followings as f
       where f.followable_id = p.merchant_id and f.followable_type = 'Merchant' and f.user_id = ?
    )

Answer 4

SELECT * FROM products p
LEFT JOIN favorites ON products.id = favorites.favorable_id and favorites.favorable_type = 'Product' AND favorites.user_id = ?
LEFT JOIN followings ON products.merchant_id = followings.followable_id and followings.followable_type = 'Merchant' AND followings.user_id = ?
WHERE favorites.user_id is not null or followings.user_id is not null

Answer 5

你可以试试这个：

select p.*
from products as p
where
p.id in (
       select f.favorable_id
       from favorites as f
       where  f.favorable_type = 'Product' and f.user_id = ?
)
or p.merchant_id in ( 
       select f.followable_id
       from followings as f
       where  f.followable_type = 'Merchant' and f.user_id = ?
)

SQL使用union在三个表之间保持连接

5 个答案: