SQL 如何从postgres中的查询中提取小时
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How to extract hour from query in postgres
提问by redneb
I have timestamp in my table and i want to extract only hour from it. I search and find a extract function but unable to use as a query. Do i need to convert first timestamp in varchar and then extract hour from it? Here is my query:
我的表中有时间戳，我只想从中提取小时。我搜索并找到了提取功能，但无法用作查询。我是否需要在 varchar 中转换第一个时间戳，然后从中提取小时？这是我的查询：
select extract(hour from timestamp '2001-02-16 20:38:40') // example
actual query:
实际查询：
select extract(hour from timestamp observationtime) from smartvakt_device_report
回答by redneb
The following should work
以下应该工作
select extract(hour from observationtime) from smartvakt_device_report
回答by Mureinik
The word timezoneis redundant (read: wrong). You just need to give the column's name. E.g.:
这个词timezone是多余的（读：错误）。您只需要提供列的名称。例如：
db=> select extract(hour from observationtime) from smartvakt_device_report;
date_part
-----------
19
(1 row)
