From: Tom Lane <tgl@sss.pgh.pa.us>
To: sean.johnston@edgeintelligence.com
cc: pgsql-bugs@postgresql.org, Robert Haas <robertmhaas@gmail.com>,
        Jeevan Chalke <jeevan.chalke@enterprisedb.com>,
        Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Subject: Re: BUG #14890: Error grouping by same column twice using FDW
In-reply-to: <20171107134948.1508.94783@wrigleys.postgresql.org>
References: <20171107134948.1508.94783@wrigleys.postgresql.org>
Comments: In-reply-to sean.johnston@edgeintelligence.com
	message dated "Tue, 07 Nov 2017 13:49:48 +0000"
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Date: Tue, 07 Nov 2017 17:29:41 -0500
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sean.johnston@edgeintelligence.com writes:
> select col1, col1 from loop_tbl group by 1, 2;
> psql:t.sql:7: ERROR:  targetlist item has multiple sortgroupref labels

This is the fault of commit 7012b132d ("Push down aggregates to remote
servers"), which imagined that postgres_fdw can use
apply_pathtarget_labeling_to_tlist() for situations well beyond that
function's limited abilities.  I kinda suspect that foreign_grouping_ok()
has got more bugs than this with complicated sortgroupref situations, too;
its willingness to scribble on the sortgrouprefs doesn't look like a great
idea to me.

			regards, tom lane


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