如何在postgresql中用“时间”字段按小时分组？
[英]how do I group by by hour in postgresql with a “time” field?
问题描述
I have a table with a column ctime of type time without time zone . 
我有一个表格，列time without time zone类型为ctime ， time without time zone 。
| cdate | ctime
+------------+----------
| 2016-12-24 | 12:02:17
| 2016-12-24 | 12:02:32
| 2016-12-24 | 12:03:00
| 2016-12-24 | 12:02:10
I would like to group by both cdate and ctime but would like for ctime to count only hours. 我想将cdate和ctime cdate ，但希望ctime只计算几个小时。
2 个解决方案
解决方案1
40 已采纳 2017-02-08 16:08:05
使用date_trunc ：
group by cdate, date_trunc('hour', ctime)
解决方案2
14 2018-04-18 02:40:14
I think date_part('hour', ctime) is a better choice if you just want to group based on the hour. 我认为如果你只想根据小时进行分组date_part('hour', ctime)是一个更好的选择。
date_part('hour', timestamp '2001-02-16 20:38:40') ---> 20
date_trunc('hour', interval '2 days 3 hours 40 minutes') ---> 2 days 03:00:00
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