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Re: How do you compare (NULL) and (non-NULL)?

From: Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>
To: Wei Weng <wweng(at)kencast(dot)com>
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: How do you compare (NULL) and (non-NULL)?
Date: 2004-10-26 20:48:48
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-sql
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.

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