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
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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

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