Postgresql - 窗口函數集合

Question

我試圖按產品類型查找每月新用戶的數量。但是，我仍然收到要求在集合函數中使用的錯誤cnt。

SELECT EXTRACT(MONTH FROM date) AS month 
FROM (SELECT users.date, 
      COUNT(*) OVER(PARTITION BY product_type) AS cnt FROM users) AS u 
GROUP BY month 
ORDER BY cnt DESC; 

Answer 1

這似乎是一個非常奇怪的構造。以下是不使用窗口功能的方法：

select date_trunc('month', date) as yyyymm, product_id, count(*) 
from (select distinct on (u.userid) u.* 
     from users u 
     order by u.userid, u.date 
    ) u 
group by date_trunc('month', date), product_id 
order by yyyymm, product_id;