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From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
To: Michael Paquier <michael.paquier@gmail.com>
Cc: Jaime Casanova <jaime.casanova@2ndquadrant.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] generated columns
Date: Thu, 1 Feb 2018 09:29:09 -0500
Message-ID: <bf9c8765-1aa0-432a-442e-45f715ebe4e7@2ndquadrant.com> (raw)
In-Reply-To: <20180131131804.GB1586@paquier.xyz>
References: <b151f851-4019-bdb1-699e-ebab07d2f40a@2ndquadrant.com>
	<CAJGNTeOxeQPFpEr35PME4yLayRzP_wwzt70kFrPztSTWHf-HDA@mail.gmail.com>
	<CAJGNTeM+MCjA4dBhAdjJ-vR_CwY3u65cCcc+KvnahzLHZjxjbw@mail.gmail.com>
	<1bc948f8-3bab-6c54-50af-c0723a75b85f@2ndquadrant.com>
	<20180116063546.GA3679@paquier.xyz>
	<48502d9b-60c4-5b10-40a2-e34f562132b4@2ndquadrant.com>
	<20180119051804.GC12826@paquier.xyz>
	<2e3d5147-16f8-af0f-00ab-4c72cafc896f@2ndquadrant.com>
	<20180131131804.GB1586@paquier.xyz>

On 1/31/18 08:18, Michael Paquier wrote:
>> This also raises a question how a row type with generated columns should
>> behave.  I think a generation expression is a property of a table, so it
>> does not apply in a row type.  (Just like a default is a property of a
>> table and does not apply in row types.)
> 
> Hm.  Identity columns and default columns are part of rowtypes. STORED
> columns can alsobe part of a row type with little effort, so in order to
> be consistent with the all the existing behaviors, it seems to me that
> virtually-generated columns should be part of it as well.  I have
> compiled in the attached SQL file how things behave with your
> patch.  Only virtually-generated columns show a blank value.
> 
> A empty value is unhelpful for the user, which brings a couple of
> possible approaches:
> 1) Make virtual columns part of a row type, which would make it
> consistent with all the other types.

That would be nice.  I'm going to study this some more to see what can
be done.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services




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