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From: Tom Lane <[email protected]>
To: Michael Herold <[email protected]>
Cc: [email protected]
Subject: Re: ARRAY[1] || NULL <> array_append(ARRAY[1], NULL)
Date: Thu, 09 Jul 2015 10:00:57 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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Michael Herold <[email protected]> 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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