Date: Tue, 26 Oct 2004 13:48:48 -0700 (PDT)
From: Stephan Szabo <sszabo@megazone.bigpanda.com>
To: Wei Weng <wweng@kencast.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: How do you compare (NULL) and (non-NULL)?
In-Reply-To: <417EB238.1000109@kencast.com>
Message-ID: <20041026134508.N5021@megazone.bigpanda.com>
References: <417EB238.1000109@kencast.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII

On Tue, 26 Oct 2004, Wei Weng wrote:

> In the following query
>
> SELECT Parent FROM Channels ORDER BY Parent ASC;
>
> If I have a couple of (NULL)s in the field [Parent], they will be listed at
> the bottom of the query result.
>
> Is it because PostgreSQL considers (NULL) as the biggest value? If I run the
> same query under MSSQL Server 2000, I get the exact opposite result
> regarding the order of (NULL)s and (non-NULL) values. They are listed at the
> very beginning of the query result.

The spec basically says (IIRC) that implementations must either treat all
nulls as greater than all non-nulls for ordering or less than all
non-nulls for ordering, but that different implementations may choose
different choices.  I think the most recent version (at least) provides an
option to specify which way to handle nulls, but we don't support that as
far as I know.