我有一个表,其中有一列的数据类型为 timestamp without time zone
,我试图在给定时区将其转换为 timestamp without time zone。
这些是我的 Postgres 9.3 设置
select current_setting('TIMEZONE');
current_setting
-----------------
Hongkong
select * from pg_timezone_names where name = 'Hongkong';
name | abbrev | utc_offset | is_dst
----------+--------+------------+--------
Hongkong | HKT | 08:00:00 | f
这是我将其转换为 HKT 的操作:
-- this SQL gives me what I expected
select '2015-01-05 12:00:00'::timestamp without time zone
at time zone 'UTC'
at time zone 'HKT';
---------------------
2015-01-05 20:00:00
-- Shouldn't this produce the same result with the above one?
-- How do I make this work?
-- Don't tell me to change it to UTC-08:00 ...
select '2015-01-05 12:00:00'::timestamp without time zone
at time zone 'UTC'
at time zone 'UTC+08:00';
---------------------
2015-01-05 04:00:00 -- WHY?
最佳答案
这背后的原因是为什么你真的不应该在 PostgreSQL 中使用时区偏移量(除非你确切地知道你在做什么)。
时区'UTC+08:00'
是POSIX风格的时区规范,'Hongkong'
是准确的时区名称, 'HKT'
是(其中之一)它的缩写。
pg_timezone_names
系统 View 的utc_offset
列是defined是 UTC 的偏移量(正数表示格林威治的东)。
但是在POSIX风格的时区规范中,偏移部分是different :
... Another issue to keep in mind is that in POSIX time zone names, positive offsets are used for locations west of Greenwich. Everywhere else, PostgreSQL follows the ISO-8601 convention that positive timezone offsets are east of Greenwich.
因此,您应该使用:
- 时区缩写,如果您想自己处理夏令时规则,
- 准确的时区名称,其他任何地方(首选)。
In short, this is the difference between abbreviations and full names: abbreviations represent a specific offset from UTC, whereas many of the full names imply a local daylight-savings time rule, and so have two possible UTC offsets.
To complicate matters, some jurisdictions have used the same timezone abbreviation to mean different UTC offsets at different times; for example, in Moscow MSK has meant UTC+3 in some years and UTC+4 in others. PostgreSQL interprets such abbreviations according to whatever they meant (or had most recently meant) on the specified date; but, as with the EST example above, this is not necessarily the same as local civil time on that date.
但最简单的解决方案是使用timestamp with time zone
:您已经将TimeZone
设置为'Hongkong'
,所以timestamp with time zone
值将以该时区显示给您的 (PostgreSQL) 客户端。
set time zone 'Hongkong';
select current_setting('TimeZone') TimeZone,
dt original,
dt AT TIME ZONE 'UTC' AT TIME ZONE 'UTC+08:00' "UTC+08:00",
dt AT TIME ZONE 'UTC' AT TIME ZONE 'UTC+8' "UTC+8",
dt AT TIME ZONE 'UTC' AT TIME ZONE 'UTC-8' "UTC-8",
dt AT TIME ZONE 'UTC' AT TIME ZONE INTERVAL '+08:00' "INTERVAL +08:00",
dt AT TIME ZONE 'UTC' AT TIME ZONE 'HKT' "HKT",
dt AT TIME ZONE 'UTC' AT TIME ZONE 'Hongkong' "Hongkong",
dt AT TIME ZONE 'UTC' "with time zone"
from (values (timestamp '2015-01-05 12:00:00')) v(dt);
-- TIMEZONE | ORIGINAL | UTC+08:00
-- ---------+---------------------+--------------------
-- Hongkong | 2015-01-05 12:00:00 | 2015-01-05 04:00:00
-- UTC+8 | UTC-8 | INTERVAL +08:00
-- --------------------+---------------------+--------------------
-- 2015-01-05 04:00:00 | 2015-01-05 20:00:00 | 2015-01-05 20:00:00
-- HKT | HONGKONG | WITH TIME ZONE
-- --------------------+---------------------+-----------------------
-- 2015-01-05 20:00:00 | 2015-01-05 20:00:00 | 2015-01-05 20:00:00+08
关于postgresql - 将时间戳转换为Postgres中特定时区的时间戳,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/27790859/