From: Tom Lane <tgl@sss.pgh.pa.us>
To: Michael Herold <quabla@hemio.de>
cc: pgsql-docs@postgresql.org
Subject: Re: ARRAY[1] || NULL <> array_append(ARRAY[1], NULL)
In-reply-to: <559DC0CE.90900@hemio.de>
References: <559DC0CE.90900@hemio.de>
Comments: In-reply-to Michael Herold <quabla@hemio.de>
 message dated "Thu, 09 Jul 2015 02:31:10 +0200"
Date: Thu, 09 Jul 2015 10:00:57 -0400
Message-ID: <32402.1436450457@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-docs-owner@postgresql.org

Michael Herold <quabla@hemio.de> writes:
> A few minutes ago I got bitten by the following PostgreSQL (9.4) behavior
> SELECT ARRAY[1] || NULL, array_append(ARRAY[1], NULL);
>   ?column? | array_append
> ----------+--------------
>   {1}      | {1,NULL}

> I expected that array_append and || are equivalent in this case but 
> obviously they are not.

Yeah, the first case turns out to be array_cat not array_append.

> Sure, this is not too surprising since "||" has 
> to guess which operation is appropriate. However, I would have highly 
> appreciated ARRAY[1,2] || NULL as an example in [Table 9-45].

Hm.  I don't think there is really room for such an example in that table,
and certainly not room for a discursive discussion.  What would make more
sense to me is to add a paragraph and example concerning this issue at the
bottom of section 8.15.4, right after array_append and array_cat are
introduced.  Since there's already a pointer to 8.15 just below that
table, people would hopefully find the example from that vicinity as well.

Seem reasonable?

			regards, tom lane


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