填补 PostgreSQL 上 SQL 查询中缺失的日期空白

Question

我有一张桌子messages，看起来像：

status	created_at	updated_at
sent	timestamp	timestamp
queued	timestamp	timestamp
failed	timestamp	timestamp

我想要一个以易于绘制图表的方式输出值的查询，我想出了这个查询：

SELECT date_trunc('hour', created_at) as hour_created, count(created_at), status 
FROM messages 
WHERE created_at >= current_timestamp - interval '1 day' 
GROUP BY (status, hour_created)

该查询输出以下内容：

hour_created	count	status
2021-10-11 08:00:00-04	10	sent
2021-10-11 09:00:00-04	95	queued
2021-10-11 10:00:00-04	174	sent
2021-10-11 12:00:00-04	1	sent
2021-10-11 13:00:00-04	1	queued
2021-10-11 13:00:00-04	2	sent
2021-10-11 14:00:00-04	1	sent
2021-10-11 18:00:00-04	2	sent

注意小时数的差距，我想用所有可能的状态（排队、失败和发送）和零来填充那些时间

Answer 1

您可以使用生成系列：

select date_trunc('hour', created_at) as hour_created, count(created_at), status 
from generate_series(date_trunc('hour',current_timestamp) - interval '1 day' ,date_trunc('hour',current_timestamp), '1 hour') intervals (cdate)
cross join (select * from (values ('failed'),('queued'),('sent')) s (status)) statuses
join messages t
on t.status = statuses.status
and t.created_at = intervals.cdate
WHERE created_at >= current_timestamp - interval '1 day' 
GROUP BY statuses.status, intervals.cdate