Postgresql-窗口函数聚合

我正在尝试按产品类型查找每月新用户的数量。但是，我继续收到一个错误，请求在聚合函数中使用

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;

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这似乎是一个非常奇怪的结构。下面是一个不使用窗口函数的方法：

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;

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编辑您的问题并提供示例数据和所需结果。