From: Tom Lane <tgl@sss.pgh.pa.us>
To: Vik Fearing <vik@postgresfriends.org>
cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
        Thomas Munro <thomas.munro@gmail.com>,
        Petr Fedorov <petr.fedorov@phystech.edu>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Since '2001-09-09 01:46:40'::timestamp microseconds are lost when
 extracting epoch
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Comments: In-reply-to Vik Fearing <vik@postgresfriends.org>
	message dated "Mon, 25 May 2020 18:01:07 +0200"
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Date: Mon, 25 May 2020 12:40:27 -0400
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Vik Fearing <vik@postgresfriends.org> writes:
> On 5/25/20 3:28 PM, Peter Eisentraut wrote:
>> I looked into this (changing the return types of date_part()/extract()
>> from float8 to numeric).

> I think what would be better is to have a specific date_part function
> for each part and have extract translate to the appropriate one.

Doesn't really work for upwards compatibility with existing views,
which will have calls to date_part(text, ...) embedded in them.

Actually, now that I think about it, changing the result type of
date_part() is likely to be problematic anyway for such cases.
It's not going to be good if pg_upgrade's dump/restore of a view
results in a new output column type; especially if it's a
materialized view.

So maybe what we'd have to do is leave date_part() alone for
legacy compatibility, and invent new functions that the extract()
syntax would now be translated to.  While at it, maybe we could
fix things so that the syntax reverse-lists the same way instead
of injecting Postgres-isms...

			regards, tom lane