Postgresql 亚马逊红移中的每月保留

我试图在

Amazon Redshift

中计算每月的保留率，并提出了以下查询：

查询1

SELECT EXTRACT(year FROM activity.created_at) AS Year,
       EXTRACT(month FROM activity.created_at) AS Month,
       COUNT(DISTINCT activity.member_id) AS active_users,
       COUNT(DISTINCT future_activity.member_id) AS retained_users,
       COUNT(DISTINCT future_activity.member_id) / COUNT(DISTINCT activity.member_id)::float AS retention
FROM ads.fbs_page_view_staging activity
  LEFT JOIN ads.fbs_page_view_staging AS future_activity
         ON activity.mongo_id = future_activity.mongo_id
AND datediff ('month',activity.created_at,future_activity.created_at) = 1
GROUP BY Year,
         Month
ORDER BY Year,
         Month

出于某种原因，此查询返回

zero

保留的用户

和

zero

保留

。我非常感谢任何关于为什么会发生这种情况的帮助，或者一个完全不同的关于每月保留金的查询会起作用

我根据另一篇SO帖子修改了查询，如下所示：

查询2

WITH t AS (
   SELECT member_id
         ,date_trunc('month', created_at) AS month
         ,count(*) AS item_transactions
         ,lag(date_trunc('month', created_at)) OVER (PARTITION BY  member_id
                                           ORDER BY date_trunc('month', created_at)) 
          = date_trunc('month', created_at) - interval '1 month'
            OR NULL AS repeat_transaction
   FROM   ads.fbs_page_view_staging
   WHERE  created_at >= '2016-01-01'::date
   AND    created_at <  '2016-04-01'::date -- time range of interest.
   GROUP  BY 1, 2
   )
SELECT month
      ,sum(item_transactions) AS num_trans
      ,count(*) AS num_buyers
      ,count(repeat_transaction) AS repeat_buyers
      ,round(
          CASE WHEN sum(item_transactions) > 0
             THEN count(repeat_transaction) / sum(item_transactions) * 100
             ELSE 0
          END, 2) AS buyer_retention
FROM   t
GROUP  BY 1
ORDER  BY 1;

我觉得

query2

会比

query1

更好，所以我更愿意修复这个错误

---

任何帮助都将不胜感激。

查询1看起来不错。我试过类似的。见下文。您正在表（ads.fbs\u page\u view\u staging）和同一列（在创建时）上使用自联接。假设mongo_id是唯一的，

datediff（'month'..）

将始终返回0，而

datediff（'month'，activity.created_at，future_activity.created_at）=1将始终为false

-- Count distinct events of join_col_id that have lapsed for one month.
SELECT count(distinct E.join_col_id) dist_ct
FROM public.fact_events E
JOIN public.dim_table Z
  ON E.join_col_id = Z.join_col_id
WHERE datediff('month', event_time, sysdate) = 1;

-- 2771654 -- dist_ct

我认为查询1的问题在于，您已将区间条件
datediff（'month'，activity.created\u at，future\u activity.created\u at）=1
放入联接中。我不认为那样行得通。因此连接失败，因此连接右侧的值为NULL，导致计数为零。当您将条件移动到“WHERE”时会发生什么？完全正确，我加入了错误的列，应该是
member\u id
，而不是
mongo\u id
。我犯了愚蠢的错误。谢谢你指出这一点。
-- Count distinct events of join_col_id that have lapsed for one month.
SELECT count(distinct E.join_col_id) dist_ct
FROM public.fact_events E
JOIN public.dim_table Z
  ON E.join_col_id = Z.join_col_id
WHERE datediff('month', event_time, sysdate) = 1;

-- 2771654 -- dist_ct