From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: pgsql-hackers@postgresql.org
Subject: Re: Implement targetlist SRFs using ROWS FROM() (was Changed SRF in
 targetlist handling)
In-reply-to: <20160827214829.zo2dfb5jaikii5nw@alap3.anarazel.de>
References: <20160523005327.v2tr7obytitxcnna@alap3.anarazel.de>
 <20160822214023.aaxz5l4igypowyri@alap3.anarazel.de>
 <20160827214829.zo2dfb5jaikii5nw@alap3.anarazel.de>
Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Sat, 27 Aug 2016 14:48:29 -0700"
Date: Mon, 12 Sep 2016 11:29:37 -0400
Message-ID: <3999.1473694177@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

Andres Freund <andres@anarazel.de> writes:
> 0002-Shore-up-some-weird-corner-cases-for-targetlist-SRFs.patch
>   Forbid UPDATE ... SET foo = SRF() and ORDER BY / GROUP BY containing
>   SRFs that would change the number of returned rows.  Without the
>   latter e.g. SELECT 1 ORDER BY generate_series(1,10); returns 10 rows.

I'm on board with disallowing SRFs in UPDATE, because it produces
underdetermined and unspecified results; but the other restriction
seems 100% arbitrary.  There is no semantic difference between
	SELECT a, b FROM ... ORDER BY srf();
and
	SELECT a, b, srf() FROM ... ORDER BY 3;
except that in the first case the ordering column doesn't get returned to
the client.  I do not see why that's so awful that we should make it fail
after twenty years of allowing it.  And I certainly don't see why there
would be an implementation reason why we couldn't support it anymore
if we can still do the second one.

			regards, tom lane


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