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* Empty array IS NULL?
@ 2004-06-28 16:01 Markus Bertheau <twanger@bluetwanger.de>
2004-06-28 16:26 ` Re: Empty array IS NULL? Joe Conway <mail@joeconway.com>
2004-06-28 19:05 ` Re: Empty array IS NULL? Greg Stark <gsstark@mit.edu>
0 siblings, 2 replies; 6+ messages in thread
From: Markus Bertheau @ 2004-06-28 16:01 UTC (permalink / raw)
To: pgsql-sql
Hi,
is the empty array representable in PostgreSQL, and is it
distinguishable from NULL?
oocms=# SELECT ARRAY[1, 2];
array
-------
{1,2}
(1 запись)
oocms=# SELECT '{1, 2}'::INT[];
int4
-------
{1,2}
(1 запись)
oocms=# SELECT ARRAY[];
ERROR: syntax error at or near "]" at character 14
oocms=# SELECT '{}'::INT[];
int4
------
{}
(1 запись)
oocms=# SELECT ARRAY(SELECT 1 UNION SELECT 2);
?column?
----------
{1,2}
(1 запись)
oocms=# SELECT ARRAY(SELECT 1 WHERE FALSE);
?column?
----------
(1 запись)
--
Markus Bertheau <twanger@bluetwanger.de>
^ permalink raw reply [nested|flat] 6+ messages in thread
* Re: Empty array IS NULL?
2004-06-28 16:01 Empty array IS NULL? Markus Bertheau <twanger@bluetwanger.de>
@ 2004-06-28 16:26 ` Joe Conway <mail@joeconway.com>
2004-06-28 17:06 ` Re: Empty array IS NULL? Markus Bertheau <twanger@bluetwanger.de>
1 sibling, 1 reply; 6+ messages in thread
From: Joe Conway @ 2004-06-28 16:26 UTC (permalink / raw)
To: Markus Bertheau <twanger@bluetwanger.de>; +Cc: pgsql-sql
Markus Bertheau wrote:
> is the empty array representable in PostgreSQL, and is it
> distinguishable from NULL?
Yes, and yes.
regression=# select '{}'::int[];
int4
------
{}
(1 row)
regression=# select NULL::int[];
int4
------
(1 row)
Since NULL array elements are not currently supported, attempting to
construct an array with a NULL element results in NULL, not an empty array.
Joe
^ permalink raw reply [nested|flat] 6+ messages in thread
* Re: Empty array IS NULL?
2004-06-28 16:01 Empty array IS NULL? Markus Bertheau <twanger@bluetwanger.de>
2004-06-28 16:26 ` Re: Empty array IS NULL? Joe Conway <mail@joeconway.com>
@ 2004-06-28 17:06 ` Markus Bertheau <twanger@bluetwanger.de>
2004-06-28 17:56 ` Re: Empty array IS NULL? Joe Conway <mail@joeconway.com>
0 siblings, 1 reply; 6+ messages in thread
From: Markus Bertheau @ 2004-06-28 17:06 UTC (permalink / raw)
To: Joe Conway <mail@joeconway.com>; +Cc: pgsql-sql
В Пнд, 28.06.2004, в 18:26, Joe Conway пишет:
> Markus Bertheau wrote:
> > is the empty array representable in PostgreSQL, and is it
> > distinguishable from NULL?
>
> Yes, and yes.
>
> Since NULL array elements are not currently supported, attempting to
> construct an array with a NULL element results in NULL, not an empty array.
Thanks.
How do I specify an empty array with the standard syntax?
--
Markus Bertheau <twanger@bluetwanger.de>
^ permalink raw reply [nested|flat] 6+ messages in thread
* Re: Empty array IS NULL?
2004-06-28 16:01 Empty array IS NULL? Markus Bertheau <twanger@bluetwanger.de>
2004-06-28 16:26 ` Re: Empty array IS NULL? Joe Conway <mail@joeconway.com>
2004-06-28 17:06 ` Re: Empty array IS NULL? Markus Bertheau <twanger@bluetwanger.de>
@ 2004-06-28 17:56 ` Joe Conway <mail@joeconway.com>
0 siblings, 0 replies; 6+ messages in thread
From: Joe Conway @ 2004-06-28 17:56 UTC (permalink / raw)
To: Markus Bertheau <twanger@bluetwanger.de>; +Cc: pgsql-sql
Markus Bertheau wrote:
> How do I specify an empty array with the standard syntax?
>
Actually, up until the 7.4 release, the array literal syntax was the
*only* syntax (i.e. '{...}'). The newer array constructor expression
(i.e. ARRAY[...]) does not yet support creating empty arrays -- there
are some non-trivial technical difficulties to be solved. Unfortunately
that won't change in the upcoming 7.5 either :( -- perhaps for 7.6.
Joe
^ permalink raw reply [nested|flat] 6+ messages in thread
* Re: Empty array IS NULL?
2004-06-28 16:01 Empty array IS NULL? Markus Bertheau <twanger@bluetwanger.de>
@ 2004-06-28 19:05 ` Greg Stark <gsstark@mit.edu>
1 sibling, 0 replies; 6+ messages in thread
From: Greg Stark @ 2004-06-28 19:05 UTC (permalink / raw)
To: Markus Bertheau <twanger@bluetwanger.de>; +Cc: pgsql-sql
Markus Bertheau <twanger@bluetwanger.de> writes:
> oocms=# SELECT ARRAY(SELECT 1 WHERE FALSE);
> ?column?
> ----------
>
This one seems strange to me. Shouldn't it result in an empty array?
--
greg
^ permalink raw reply [nested|flat] 6+ messages in thread
* Re: Empty array IS NULL?
@ 2004-06-28 17:56 Joe Conway <mail@joeconway.com>
0 siblings, 0 replies; 6+ messages in thread
From: Joe Conway @ 2004-06-28 17:56 UTC (permalink / raw)
To: Markus Bertheau <twanger@bluetwanger.de>; +Cc: pgsql-sql
Markus Bertheau wrote:
> How do I specify an empty array with the standard syntax?
Actually, up until the 7.4 release, the array literal syntax was the
*only* syntax (i.e. '{...}'). The newer array constructor expression
(i.e. ARRAY[...]) does not yet support creating empty arrays -- there
are some non-trivial technical difficulties to be solved. Unfortunately
that won't change in the upcoming 7.5 either :( -- perhaps for 7.6.
Joe
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^ permalink raw reply [nested|flat] 6+ messages in thread
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Thread overview: 6+ messages (download: mbox mbox.gz follow: Atom feed)
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2004-06-28 16:01 Empty array IS NULL? Markus Bertheau <twanger@bluetwanger.de>
2004-06-28 16:26 ` Joe Conway <mail@joeconway.com>
2004-06-28 17:06 ` Markus Bertheau <twanger@bluetwanger.de>
2004-06-28 17:56 ` Joe Conway <mail@joeconway.com>
2004-06-28 19:05 ` Greg Stark <gsstark@mit.edu>
2004-06-28 17:56 Re: Empty array IS NULL? Joe Conway <mail@joeconway.com>
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