，Postgres的查詢 - 找到開始和周結束之差，每週

Question

我有被髮送daily領域

total_user_count, sent_at

列user_report。

我試圖找到total new users per week，其被定義爲

difference in user count from the beginning of the week to the ending of the week.

我似乎遇到了問題，雖然制定此查詢，我有什麼是

SELECT DATE_TRUNC('day', sent_at AT TIME ZONE '+08') as date, total_user_count 
FROM user_state_report 
WHERE timestamptz_cmp(DATE_TRUNC('week', sent_at AT TIME ZONE '+08') , DATE_TRUNC('day', sent_at AT TIME ZONE '+08'))=0 
ORDER BY TIMESTAMP 

哪給我每週的總用戶數。但我想每週新註冊，而不是總數量

理想輸出：

Date [monday of the week X], users registered in this week 14-08-2017 300 21-08-2017 400

謝謝！ :)

Answer 1

你應該能夠用滯後函數做到這一點。喜歡的東西：

SELECT date, total_user_count - COALESCE(LAG(total_user_count) OVER(order by date),0) AS new_users_registered from 
(SELECT DATE_TRUNC('day', sent_at AT TIME ZONE '+08') as date, total_user_count 
FROM user_state_report 
WHERE timestamptz_cmp(DATE_TRUNC('week', sent_at AT TIME ZONE '+08') , DATE_TRUNC('day', sent_at AT TIME ZONE '+08'))=0 
ORDER BY sent_at) l 

BTW我改變了你的ORDER BY TIMESTAMP到ORDER BY sent_at，因爲我沒有undertstand如何你一個工作！