使用postgresql时计数*太慢

我注意到，当涉及到深度SQL时，COUNT*from表并不是一个优化的查询

下面是我正在使用的sql

SELECT COUNT(*) FROM "items"
INNER JOIN (
  SELECT c.* FROM companies c LEFT OUTER JOIN company_groups ON c.id = company_groups.company_id
  WHERE company_groups.has_restriction IS NULL OR company_groups.has_restriction = 'f' OR company_groups.company_id = 1999 OR company_groups.group_id IN ('3','2')
  GROUP BY c.id
) AS companies ON companies.id = stock_items.vendor_id
LEFT OUTER JOIN favs ON items.id = favs.item_id AND favs.user_id = 999 AND favs.is_visible = TRUE
WHERE "items"."type" IN ('Fashion') AND "items"."visibility" = 't' AND "items"."is_hidden" = 'f' AND (items.depth IS NULL OR (items.depth >= '0' AND items.depth <= '100')) AND (items.table IS NULL OR (items.table >= '0' AND items.table <= '100')) AND (items.company_id NOT IN (199,200,201))

请建议我如何使它工作得更快

注意：所有列都有索引，如类型、可见性、是否隐藏、表格、深度等

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提前谢谢

好吧，您有两个部分可以选择查询中的所有select*，也许您可以限制它，看看它是否有用，例如：

SELECT COUNT(OneSpecificColumn)
FROM "items"
INNER JOIN
  ( SELECT c.(AnotherSpecificColumn)
   FROM companies c
   LEFT OUTER JOIN company_groups ON c.id = company_groups.company_id
   WHERE company_groups.has_restriction IS NULL
     OR company_groups.has_restriction = 'f'
     OR company_groups.company_id = 1999
     OR company_groups.group_id IN ('3',
                                    '2')
   GROUP BY c.id) AS companies ON companies.id = stock_items.vendor_id
LEFT OUTER JOIN favs ON items.id = favs.item_id
AND favs.user_id = 999
AND favs.is_visible = TRUE
WHERE "items"."type" IN ('Fashion')
  AND "items"."visibility" = 't'
  AND "items"."is_hidden" = 'f'
  AND (items.depth IS NULL
       OR (items.depth >= '0'
           AND items.depth <= '100'))
  AND (items.table IS NULL
       OR (items.table >= '0'
           AND items.table <= '100'))
  AND (items.company_id NOT IN (199,
                                200,
                                201))

---

您还可以检查这些左连接是否都是必需的，内部连接的成本更低，并且可以加快搜索速度

大部分时间花在项目的顺序扫描上，这是无法改进的，因为您几乎需要表中的所有行

因此，改进查询的唯一方法是

查看项目是否缓存在内存中

获得更快的存储速度

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你是在使用kaminari之类的分页宝石，还是will_paginate会射入你的腿？@PavelMikhailyuk我们确实安装了kaminari，但为此我们没有使用kaminari。相反，我们使用的是限制和抵消，其目的是避免依赖关系。通常计数用于分页。所以您必须将分页实现从基于计数的计算页码更改为无限滚动。或者在数据库或内存中缓存总计数。您好@eliamelfior我尝试了您的1建议，即限制列，但sql仍然需要4043毫秒。

SELECT COUNT(OneSpecificColumn)
FROM "items"
INNER JOIN
  ( SELECT c.(AnotherSpecificColumn)
   FROM companies c
   LEFT OUTER JOIN company_groups ON c.id = company_groups.company_id
   WHERE company_groups.has_restriction IS NULL
     OR company_groups.has_restriction = 'f'
     OR company_groups.company_id = 1999
     OR company_groups.group_id IN ('3',
                                    '2')
   GROUP BY c.id) AS companies ON companies.id = stock_items.vendor_id
LEFT OUTER JOIN favs ON items.id = favs.item_id
AND favs.user_id = 999
AND favs.is_visible = TRUE
WHERE "items"."type" IN ('Fashion')
  AND "items"."visibility" = 't'
  AND "items"."is_hidden" = 'f'
  AND (items.depth IS NULL
       OR (items.depth >= '0'
           AND items.depth <= '100'))
  AND (items.table IS NULL
       OR (items.table >= '0'
           AND items.table <= '100'))
  AND (items.company_id NOT IN (199,
                                200,
                                201))