PostgreSQL-窗口函數匯總

Question

我正在嘗試按產品類型查找每月的新用戶數。 但是，我繼續收到錯誤消息，要求在聚合函數中使用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。 這是一種不使用窗口函數的方法：

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;