pg.ddx.io pgsql-sql@postgresql.org mailing list archive
help / color / mirror / Atom feedquastions about primary key
5+ messages / 4 participants
[nested] [flat]
* quastions about primary key
@ 2003-01-24 06:44 jack <datactrl@tpg.com.au>
0 siblings, 2 replies; 5+ messages in thread
From: jack @ 2003-01-24 06:44 UTC (permalink / raw)
To: pgsql-sql
Is that possible to have a two columns primary key on a table with null
value on second column?
Jack
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: quastions about primary key
@ 2003-01-24 10:04 Tomasz Myrta <jasiek@klaster.net>
parent: jack <datactrl@tpg.com.au>
1 sibling, 0 replies; 5+ messages in thread
From: Tomasz Myrta @ 2003-01-24 10:04 UTC (permalink / raw)
To: jack <datactrl@tpg.com.au>; +Cc: pgsql-sql
jack wrote:
> Is that possible to have a two columns primary key on a table with null
> value on second column?
>
> Jack
Probably not, because (1,2,null,null) is unique for postresql.
Watch discussion on mailing list
about unique indexes (on which primary key is based) several days ago.
Regards,
Tomasz Myrta
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: quastions about primary key
@ 2003-01-24 15:14 Stephan Szabo <sszabo@megazone23.bigpanda.com>
parent: jack <datactrl@tpg.com.au>
1 sibling, 1 reply; 5+ messages in thread
From: Stephan Szabo @ 2003-01-24 15:14 UTC (permalink / raw)
To: jack <datactrl@tpg.com.au>; +Cc: pgsql-sql
On Fri, 24 Jan 2003, jack wrote:
> Is that possible to have a two columns primary key on a table with null
> value on second column?
No, because primary key implies not null on all columns involved
(technically I think it's that a non-deferrable primary key implies
not null on all columns involved, but we don't support deferrable ones)
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: quastions about primary key
@ 2003-01-26 02:29 jack <datactrl@tpg.com.au>
parent: Stephan Szabo <sszabo@megazone23.bigpanda.com>
0 siblings, 1 reply; 5+ messages in thread
From: jack @ 2003-01-26 02:29 UTC (permalink / raw)
To: pgsql-sql
I try use uique instead of primary key. And it works, it allows null values.
Is there any other difference between primary key and unique?
Jack
----- Original Message -----
From: "Stephan Szabo" <sszabo@megazone23.bigpanda.com>
To: "jack" <datactrl@tpg.com.au>
Cc: <pgsql-sql@postgresql.org>
Sent: Saturday, January 25, 2003 1:14 AM
Subject: Re: [SQL] quastions about primary key
> On Fri, 24 Jan 2003, jack wrote:
>
> > Is that possible to have a two columns primary key on a table with null
> > value on second column?
>
> No, because primary key implies not null on all columns involved
> (technically I think it's that a non-deferrable primary key implies
> not null on all columns involved, but we don't support deferrable ones)
>
>
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: quastions about primary key
@ 2003-01-26 04:23 Bruno Wolff III <bruno@wolff.to>
parent: jack <datactrl@tpg.com.au>
0 siblings, 0 replies; 5+ messages in thread
From: Bruno Wolff III @ 2003-01-26 04:23 UTC (permalink / raw)
To: jack <datactrl@tpg.com.au>; +Cc: pgsql-sql
On Sun, Jan 26, 2003 at 12:29:12 +1000,
jack <datactrl@tpg.com.au> wrote:
>
> I try use uique instead of primary key. And it works, it allows null values.
> Is there any other difference between primary key and unique?
I believe that the primary key is the default key for foreign key references
into a table.
^ permalink raw reply [nested|flat] 5+ messages in thread
end of thread, other threads:[~2003-01-26 04:23 UTC | newest]
Thread overview: 5+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2003-01-24 06:44 quastions about primary key jack <datactrl@tpg.com.au>
2003-01-24 10:04 ` Tomasz Myrta <jasiek@klaster.net>
2003-01-24 15:14 ` Stephan Szabo <sszabo@megazone23.bigpanda.com>
2003-01-26 02:29 ` jack <datactrl@tpg.com.au>
2003-01-26 04:23 ` Bruno Wolff III <bruno@wolff.to>
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox