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From: David Fetter <david@fetter.org>
To: Nasby, Jim <nasbyj@amazon.com>
Cc: Corey Huinker <corey.huinker@gmail.com>
Cc: surafel3000@gmail.com <surafel3000@gmail.com>
Cc: cmt@burggraben.net <cmt@burggraben.net>
Cc: pgsql-hackers@lists.postgresql.org <pgsql-hackers@lists.postgresql.org>
Subject: Re: COPY FROM WHEN condition
Date: Thu, 1 Nov 2018 01:41:55 +0100
Message-ID: <20181101004155.GI12677@fetter.org> (raw)
In-Reply-To: <5E61B32E-61CB-4EBB-BC8E-BE37DC6E79AB@amazon.com>
References: <CALAY4q_DdpWDuB5-Zyi-oTtO2uSk8pmy+dupiRe3AvAc++1imA@mail.gmail.com>
	<20181011085925.5zopu7jvxzs5c4xq@squirrel.exwg.net>
	<CALAY4q__47MCCgspPVETAeSpJYfaYGpwH2diDGp5KjfSxTma4A@mail.gmail.com>
	<CADkLM=dmvGSpZ+h_CzFoGeuzH7mZT3TLttx-ikc+UYw_e6L2jg@mail.gmail.com>
	<20181011153505.GL6157@fetter.org>
	<5E61B32E-61CB-4EBB-BC8E-BE37DC6E79AB@amazon.com>

On Wed, Oct 31, 2018 at 11:21:33PM +0000, Nasby, Jim wrote:
> On Oct 11, 2018, at 10:35 AM, David Fetter <david@fetter.org> wrote:
> > 
> >> It didn't get far, but you may want to take a look at a rejected patch for
> >> copy_srf() (set returning function)
> >> https://www.postgresql.org/message-id/CADkLM%3DdoeiWQX4AGtDNG4PsWfSXz3ai7kY%3DPZm3sUhsUeev9Bg%40mail...
> >> https://commitfest.postgresql.org/12/869/
> >> 
> >> Having a set returning function gives you the full expressiveness of SQL,
> >> at the cost of an extra materialization step.
> > 
> > I wonder whether something JIT-like could elide this. A very
> > interesting subset of such WHEN clauses could be pretty
> > straight-forward to implement in a pretty efficient way.
> 
> Are you thinking something like having a COPY command that provides
> results in such a way that they could be referenced in a FROM clause
> (perhaps a COPY that defines a cursor…)?

That would also be nice, but what I was thinking of was that some
highly restricted subset of cases of SQL in general could lend
themselves to levels of optimization that would be impractical in
other contexts.

Best,
David.
-- 
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778

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