Re: NULL values seem to short-circuit my unique index

From: Chris <dmagick(at)gmail(dot)com>
To: Matthew Wilson <matt(at)tplus1(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: NULL values seem to short-circuit my unique index
Date: 2008-09-29 02:59:59
Message-ID: 48E044AF.9040104@gmail.com
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-general

Matthew Wilson wrote:
> I'm trying to comprehend how NULL values interact with unique indexes.
> It seems like I can insert two rows with NULL values in a column with a
> unique constraint just fine.
>
> Is there something special about NULL? Can anyone post some links to
> explain what is going on?

When you think of null as "unknown", it makes sense.

Does an unknown value equal another unknown value?

http://www.postgresql.org/docs/8.3/interactive/functions-logical.html

http://www.postgresql.org/docs/8.3/interactive/functions-comparison.html

--
Postgresql & php tutorials
http://www.designmagick.com/

In response to

Responses

Browse pgsql-general by date

  From Date Subject
Next Message Tom Lane 2008-09-29 03:04:50 Re: NULL values seem to short-circuit my unique index
Previous Message Matthew Wilson 2008-09-29 02:32:56 NULL values seem to short-circuit my unique index