Re: Why can't I select un-grouped columns when grouping by a (non-primary) unique key?

From: Alberto Cabello Sánchez <alberto(at)unex(dot)es>
To: pgsql-general(at)postgresql(dot)org
Subject: Re: Why can't I select un-grouped columns when grouping by a (non-primary) unique key?
Date: 2014-09-24 17:37:10
Message-ID: 20140924193710.bd4b8c1de92a8b66ac98c297@unex.es
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On Wed, 24 Sep 2014 09:04:21 -0700
Daniel Lenski <dlenski(at)gmail(dot)com> wrote:

> If I include the primary key of a table in my GROUP BY clause, PG 9.3
> allows me to refer to other columns of that table without explicit GROUP BY:
>
> Why doesn't the same thing work with a non-NULL unique constraint?

At first sight, primary key means no grouping at all, as there are no
duplicated A.primary_key values:

SELECT A.document
FROM A
GROUP BY A.primary_key

is the same as

SELECT A.document
FROM A

--
Alberto Cabello Sánchez
<alberto(at)unex(dot)es>

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