Re: FDW: possible resjunk columns in AddForeignUpdateTargets

From: Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>
To: "Tom Lane *EXTERN*" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, "rdunklau(at)gmail(dot)com" <rdunklau(at)gmail(dot)com>
Subject: Re: FDW: possible resjunk columns in AddForeignUpdateTargets
Date: 2013-11-08 14:20:02
Message-ID: A737B7A37273E048B164557ADEF4A58B17C57B24@ntex2010i.host.magwien.gv.at
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Tom Lane wrote:
> Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at> writes:
>> I have a question concerning the Foreign Data Wrapper API:
>> I find no mention of this in the documentation, but I remember that
>> you can only add a resjunk column that matches an existing attribute
>> of the foreign table and not one with an arbitrary name or
>> definition.
>
>> Ist that right?
>
> I don't recall such a limitation offhand. It's probably true that
> you can't create Vars that don't match some declared column of the
> table, but that doesn't restrict what you put into resjunk columns
> AFAIR.

I am confused, probably due to lack of knowledge.

What I would like to do is add a custom resjunk column
(e.g. a bytea) in AddForeignUpdateTargets that carries a row identifier
from the scan state to the modify state.
Would that be possible? Can I have anything else than a Var
in a resjunk column?

Yours,
Laurenz Albe

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