From: Tom Lane <tgl@sss.pgh.pa.us>
To: greg.brown@csgi.com
cc: pgsql-docs@lists.postgresql.org
Subject: Re: pg_timezone_names
In-reply-to: <20180117171641.3623.54337@wrigleys.postgresql.org>
References: <20180117171641.3623.54337@wrigleys.postgresql.org>
Comments: In-reply-to =?utf-8?q?PG_Doc_comments_form?=
 <noreply@postgresql.org>
	message dated "Wed, 17 Jan 2018 17:16:41 +0000"
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Date: Wed, 17 Jan 2018 12:33:29 -0500
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=?utf-8?q?PG_Doc_comments_form?= <noreply@postgresql.org> writes:
> We are exporting data from postgres into another "all in one" data store,
> and i had a quick question regarding the time offsets.  The UTC_OFFSET, does
> it change when IS_DST is true/false?

Yes; utc_offset reflects the zone's current offset from UTC, so it changes
with the seasons if the zone has DST laws.

> Or do I need to take the UTC_OFFSET
> interval and then possibly add 1 more if IS_DST is true?

Prepare to be disappointed; you can't assume it works like that.
See the thread starting here:

http://mm.icann.org/pipermail/tz/2017-December/025682.html

You haven't said what it is you are hoping to accomplish, so it's
hard to say if there's some safer way to do it.

			regards, tom lane