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

On Wed, 24 Sep 2014 09:04:21 -0700
Daniel Lenski <dlenski@gmail.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@unex.es>