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From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
To: Wolfgang Walther <walther@technowledgy.de>
To: Fabien COELHO <coelho@cri.ensmp.fr>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Allow an alias to be attached directly to a JOIN ... USING
Date: Sat, 14 Nov 2020 09:52:39 +0100
Message-ID: <91c3880a-de95-324d-1d75-3ed512b221b6@2ndquadrant.com> (raw)
In-Reply-To: <88018eae-d949-be66-7fec-924213213b49@technowledgy.de>
References: <20190917173742.GA8735@alvherre.pgsql>
	<alpine.DEB.2.21.1912241908490.27864@pseudo>
	<9a5c9ed2-1dd7-8c2a-6b90-0de54f4c13a1@2ndquadrant.com>
	<8568b66d-405d-5d83-ac8c-e107f1b9f113@2ndquadrant.com>
	<d173356b-8ee7-8036-0f17-04d196494143@2ndquadrant.com>
	<88018eae-d949-be66-7fec-924213213b49@technowledgy.de>

On 2020-08-03 19:44, Wolfgang Walther wrote:
> So given this:
> 
> SELECT x.id FROM a LEFT JOIN b USING (id) AS x
> 
> will this return NULL or a.id for rows that don't match in b? This
> should definitely be mentioned in the docs and I guess a test wouldn't
> be too bad as well?

This issue is independent of the presence of the alias "x", so I don't 
think it has to do with this patch.

There is a fair amount of documentation on outer joins, so I expect that 
this is discussed there.

-- 
Peter Eisentraut
2ndQuadrant, an EDB company
https://www.2ndquadrant.com/





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