Ruby on rails RAILS SQL子查询优化

我有一个查询，如下所示：

@inventory =  Pack.find_by_sql("SELECT Packs.id, "+
" (SELECT COUNT(*) FROM Stocks WHERE (Stocks.pack_id = Packs.id AND Stocks.status = 'online'      AND Stocks.user_id = #{current_user.id})) AS online,"+
" (SELECT COUNT(*) FROM Stocks WHERE (Stocks.pack_id = Packs.id AND Stocks.status = 'offline'     AND Stocks.user_id = #{current_user.id})) AS offline,"+
" (SELECT COUNT(*) FROM Stocks WHERE (Stocks.pack_id = Packs.id AND Stocks.status = 'depositing'  AND Stocks.user_id = #{current_user.id})) AS depositing,"+
" (SELECT COUNT(*) FROM Stocks WHERE (Stocks.pack_id = Packs.id AND Stocks.status = 'withdrawing' AND Stocks.user_id = #{current_user.id})) AS withdrawing,"+
" (SELECT COUNT(*) FROM Stocks WHERE (Stocks.pack_id = Packs.id AND Stocks.status = 'selling'     AND Stocks.user_id = #{current_user.id})) AS selling,"+
" (SELECT COUNT(*) FROM Transactions WHERE (Transactions.pack_id = Packs.id AND Transactions.status = 'buying' AND Transactions.buyer_id = #{current_user.id})) AS buying"+
" FROM Packs WHERE disabled = false")

@inventory = Pack.find_by_sql("SELECT status, count(*)
                               FROM stocks
                               WHERE user_id = ?
                               GROUP BY status
                               ORDER BY status", current_user.id)

我在想有一种方法可以创建一个新的子查询，这样就可以代替

SELECT FROM Stocks

查询从存储的表中进行选择

SELECT FROM (Stocks WHERE (Stocks.pack_id = Packs.id AND Stocks.user_id = #{current_user.id}))

只能查询一次。然后将

WHERE Stocks.status=？

内容应用于该存储表

---

有什么帮助吗？

如果您想要的是各种类型的计数，那么像下面这样的代码会少得多，而且更易于阅读/维护，我想

您可以将它们拆分为不同的表，因此，对于

股票

，如下所示：

@inventory =  Pack.find_by_sql("SELECT Packs.id, "+
" (SELECT COUNT(*) FROM Stocks WHERE (Stocks.pack_id = Packs.id AND Stocks.status = 'online'      AND Stocks.user_id = #{current_user.id})) AS online,"+
" (SELECT COUNT(*) FROM Stocks WHERE (Stocks.pack_id = Packs.id AND Stocks.status = 'offline'     AND Stocks.user_id = #{current_user.id})) AS offline,"+
" (SELECT COUNT(*) FROM Stocks WHERE (Stocks.pack_id = Packs.id AND Stocks.status = 'depositing'  AND Stocks.user_id = #{current_user.id})) AS depositing,"+
" (SELECT COUNT(*) FROM Stocks WHERE (Stocks.pack_id = Packs.id AND Stocks.status = 'withdrawing' AND Stocks.user_id = #{current_user.id})) AS withdrawing,"+
" (SELECT COUNT(*) FROM Stocks WHERE (Stocks.pack_id = Packs.id AND Stocks.status = 'selling'     AND Stocks.user_id = #{current_user.id})) AS selling,"+
" (SELECT COUNT(*) FROM Transactions WHERE (Transactions.pack_id = Packs.id AND Transactions.status = 'buying' AND Transactions.buyer_id = #{current_user.id})) AS buying"+
" FROM Packs WHERE disabled = false")

@inventory = Pack.find_by_sql("SELECT status, count(*)
                               FROM stocks
                               WHERE user_id = ?
                               GROUP BY status
                               ORDER BY status", current_user.id)

请注意使用

？

防止SQL注入的重要性。此外，Ruby支持多行字符串，因此不需要引用和连接每一行

---

您可以对其他表执行类似操作。

最佳查询取决于数据分布和其他详细信息

只要子查询中的大多数

pack\u id

实际用于连接到

packs

（大多数

pack

未禁用），这是非常有效的：

在pg9.4中，您可以使用聚合筛选子句：

SELECT pack_id 
     , count(*) FILTER (WHERE status = 'online')      AS online
     , count(*) FILTER (WHERE status = 'offline')     AS offline
     , count(*) FILTER (WHERE status = 'depositing')  AS depositing
     , count(*) FILTER (WHERE status = 'withdrawing') AS withdrawing
     , count(*) FILTER (WHERE status = 'selling')     AS selling
FROM   stocks
WHERE  ... 

详情：

对数据透视表使用

交叉表（）

可以加快速度，但：

SELECT p.id
     , s.online, s.offline, s.depositing, s.withdrawing, s.selling, t.buying
FROM   packs p
LEFT   JOIN  crosstab(
   $$
   SELECT pack_id, status, count(*)::int AS ct
   FROM   stocks
   WHERE  user_id = $$ || #{current_user.id} || $$
   AND    status = ANY('{online,offline,depositing,withdrawing,selling}'::text[])
   GROUP  BY 1, 2
   ORDER  BY 1, 2
   $$
  ,$$SELECT unnest('{online,offline,depositing,withdrawing,selling}'::text[])$$
    ) s (pack_id int
      , online int
      , offline int
      , depositing int
      , withdrawing int
      , selling int
       ) USING (pack_id)
LEFT   JOIN (
   SELECT pack_id, count(*) AS buying
   FROM   transactions
   WHERE  status = 'buying'
   AND    buyer_id = #{current_user.id}
   ) t ON  t.pack_id = p.id
WHERE  NOT p.disabled;

为什么是横向的？pg9.1中是否有替代方案

---

请随时提供您的Postgres.9.1版本。我可能会在某个时候更新到9.4。这段代码可以工作，这是我通常尝试做的，但速度大约慢15倍。不过，我没有使用足够的测试数据，因此我必须添加更多数据并进行比较。@user1694853:对于性能优化，我们需要更多数据。特别是表定义、基数和值频率（什么百分比的

pack

是

禁用的
股票中有多少不同的价值。状态
？Freuquecies？等等。我添加了更多的选项。天哪，你对sql有着疯狂的了解。我需要读一些书来了解这里发生了什么，lol。谢谢你的帮助。我会在再次测试后回复你的安装一个更大的对象池。我想我应该升级到第9.4页。9.5已经发布了还是仅仅是他们的文档？@AronGreenspan:9.5是新的devel版本。请等待升级，直到它发布。