在postgresql中的子查询中使用外部查询结果

Question

我有两张桌子points,contacts而且我试图points.score按月分组每个联系人的平均值. 请注意,积分和联系人不相关,我只想要在一个月内创建的积分总和除以该月份存在的联系人数量.

所以,我需要总结按created_at月份分组的点数,我需要只计算那个月份的联系人数量.这是最后一部分让我烦恼的部分.我不确定如何在子查询中使用外部查询中的列.我试过这样的事情:

SELECT SUM(score) AS points_sum,
  EXTRACT(month FROM created_at) AS month,
  date_trunc('MONTH', created_at) + INTERVAL '1 month' AS next_month,
  (SELECT COUNT(id) FROM contacts WHERE contacts.created_at <= next_month) as contact_count
FROM points
GROUP BY month, next_month
ORDER BY month

所以,我正在提取我的积分总和的实际月份,同时,得到next_month的开头,这样我就可以说"让我知道他们创建的联系人的数量是<next_month"

但它抱怨说column next_month doesn't exist 这是可以理解的,因为子查询对外部查询一无所知.资格赛points.next_month也不起作用.

那么有人能指出我如何实现这一目标的正确方向吗？

表:

点

score | created_at
10    | "2011-11-15 21:44:00.363423"
11    | "2011-10-15 21:44:00.69667" 
12    | "2011-09-15 21:44:00.773289"
13    | "2011-08-15 21:44:00.848838"
14    | "2011-07-15 21:44:00.924152"

往来

id | created_at
6  | "2011-07-15 21:43:17.534777"
5  | "2011-08-15 21:43:17.520828"
4  | "2011-09-15 21:43:17.506452"
3  | "2011-10-15 21:43:17.491848"
1  | "2011-11-15 21:42:54.759225"

sum,month和next_month(没有subselect)

sum | month | next_month
14  | 7     | "2011-08-01 00:00:00"
13  | 8     | "2011-09-01 00:00:00"
12  | 9     | "2011-10-01 00:00:00"
11  | 10    | "2011-11-01 00:00:00"
10  | 11    | "2011-12-01 00:00:00"

Answer 1

编辑

现在有了联系人的总和.我的第一稿每月使用新的联系人,这显然不是OP想要的.

WITH c AS (
    SELECT created_at
          ,count(id) OVER (order BY created_at) AS ct
    FROM   contacts
    ), p AS (
    SELECT date_trunc('month', created_at) AS month
          ,sum(score) AS points_sum
    FROM   points
    GROUP  BY 1
    )
SELECT p.month
      ,EXTRACT(month FROM p.month) AS month_nr
      ,p.points_sum
      ,( SELECT c.ct
         FROM   c
         WHERE  c.created_at < (p.month + interval '1 month')
         ORDER  BY c.created_at DESC
         LIMIT  1) AS contacts
FROM   p
ORDER  BY 1

• 这适用于任何划过来的月数.
• 假设表中没有缺少月份points.如果您希望所有月份(包括缺少的points月份)生成带有generate_series()和LEFT JOIN 的月份列表.
• 使用窗口函数在CTE中构建运行总和.
• 两种CTE都不是严格必要的 - 仅用于性能和简化.
• 在子选择中获取contacts_count.

您的原始查询形式可以这样工作:

SELECT month
      ,EXTRACT(month FROM month) AS month_nr
      ,points_sum
      ,(SELECT count(*)
        FROM   contacts c
        WHERE  c.created_at < (p.month + interval '1 month')) AS contact_count
FROM   (
    SELECT date_trunc('MONTH', created_at) AS month
          ,sum(score) AS points_sum
    FROM   points p
    GROUP  BY 1
    ) p
ORDER  BY 1

解决错误的直接原因是将聚合放入子查询中.你以一种不可能的方式混合水平.
我希望我的变体在大桌子上稍快一些.关于较小的表不确定.如果你用测试结果报告回来会很棒.
加上一个小修复:<而不是<=.