From: Bruno Wolff III <bruno@wolff.to>
To: dev@archonet.com
Cc: pgsql-sql@postgresql.org
Subject: Re: RFC: A brief guide to nulls
Date: Wed, 15 Jan 2003 14:41:29 -0600
Message-ID: <20030115204129.GA16969@wolff.to> (raw)
In-Reply-To: <1522.192.168.1.16.1042651389.squirrel@mainbox.archonet.com>
References: <1522.192.168.1.16.1042651389.squirrel@mainbox.archonet.com>
On Wed, Jan 15, 2003 at 17:23:09 -0000,
dev@archonet.com wrote:
>
> How do nulls work?
> ==================
> There is one very important rule when dealing with nulls. The result of
> any operation or comparison, when applied to a null is null. The only
> exception is testing if a value is null.
I suggest rephrasing this to make it clear you need to use is null to
do this and that = null won't do what you expect.
> If you try to perform an operation on nulls, again the result is always
> null. So the results of all of the following are null:
The above isn't true (i.e. null op something isn't ALWAYS null). For example:
bruno=> select 't'::boolean or null;
?column?
----------
t
(1 row)
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To: pgsql-sql@postgresql.org
Cc: bruno@wolff.to, dev@archonet.com
Subject: Re: RFC: A brief guide to nulls
In-Reply-To: <20030115204129.GA16969@wolff.to>
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