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Subject: Re: ARRAY() returning NULL instead of ARRAY[] resp. {}
From: Markus Bertheau =?UTF-8?Q?=E2=98=AD?= <twanger@bluetwanger.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Joe Conway <mail@joeconway.com>, pgsql-sql@postgresql.org,
	pgsql-hackers@postgresql.org
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В Втр, 24/05/2005 в 00:06 -0400, Tom Lane пишет:
> Joe Conway <mail@joeconway.com> writes:
> > Markus Bertheau wrote:
> >> why does SELECT ARRAY(SELECT 1 WHERE FALSE) return NULL instead of
> >> ARRAY[] resp. '{}'?
> 
> > Why would you expect an empty array instead of a NULL?
> 
> I think he's got a good point, actually.  We document the ARRAY-with-
> parens-around-a-SELECT syntax as
> 
> 	The resulting one-dimensional array will have an element for
> 	each row in the subquery result, with an element type matching
> 	that of the subquery's output column.
> 
> To me, that implies that a subquery result of no rows generates a
> one-dimensional array of no elements, not a null array.

By analogy, array_upper('{}'::TEXT[], 1) should return 0 instead of
NULL.

Markus

-- 
Markus Bertheau ☭ <twanger@bluetwanger.de>