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Re: [PATCH] Provide rowcount for utility SELECTs

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Boszormenyi Zoltan <zb(at)cybertec(dot)at>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Hans-Juergen Schoenig <hs(at)cybertec(dot)at>
Subject: Re: [PATCH] Provide rowcount for utility SELECTs
Date: 2009-12-29 08:06:21
Message-ID: 603c8f070912290006h33339d4fmcb1cecfef2d43cbd@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Dec 28, 2009 at 12:10 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Boszormenyi Zoltan <zb(at)cybertec(dot)at> writes:
>> attached is a small patch that makes it possible for clients
>> to receive row count for SELECT ... INTO ... and CREATE TABLE ... AS ...
>
>> Comments?
>
> This doesn't look tremendously well thought out to me.
>
> 1. As given, the patch changes the result not only for SELECT INTO but
> for any SELECT executed in PORTAL_MULTI_QUERY context (consider SELECTs
> added by rules for example).  It seems like a pretty bad idea for the
> result of a statement to depend on context.
>
> 2. In the past we have regretted it when we made the same command tag
> sometimes have numbers attached and sometimes not (note the hack at
> the bottom of PortalRunMulti).  It doesn't seem like terribly good
> design to do that here.  On the other hand, always attaching a count
> to SELECT tags would greatly increase the risk of breaking clients.
>
>
> I'm not at all convinced that this is so useful as to justify taking
> any compatibility risks for.  People who really need that count can
> get it easily enough by breaking the command into a CREATE followed
> by INSERT/SELECT.

I don't know whether or not it's a good idea to do this for anything
in a PORTAL_MULTI_QUERY context, because I haven't really thought
through the issues.  But, it's hard for me to imagine that anyone is
depending on the command tag returned by CTAS or SELECT INTO.

Generally, I think making command tags return more useful information
is a good thing.

...Robert

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