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Message-ID: <6c21003b041119104039c88faf@mail.gmail.com>
Date: Fri, 19 Nov 2004 12:40:02 -0600
From: Don Drake <dondrake@gmail.com>
Reply-To: Don Drake <dondrake@gmail.com>
To: Richard Huxton <dev@archonet.com>
Subject: Re: NULLS and string concatenation
Cc: pgsql-sql@postgresql.org
In-Reply-To: <419E31F2.4060104@archonet.com>
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References: <6c21003b0411190912630d4afe@mail.gmail.com>
	<419E31F2.4060104@archonet.com>

On Fri, 19 Nov 2004 17:48:34 +0000, Richard Huxton <dev@archonet.com> wrote:
> Don Drake wrote:
> > select 'some text, should be null:'|| NULL
> >
> > This returns NULL and no other text.  Why is that?  I wasn't expecting
> > the "some text.." to disappear altogether.
> >
> > Is this a bug?
> 
> No. Null is "unknown" if you append unknown (null) to a piece of text,
> the result is unknown (null) too.
> 
> If you're using NULL to mean something other than unknown, you probably
> want to re-examine your reasons why.
> 

I'm using NULL to mean no value.  Logically, NULL is unknown, I agree.

I'm trying to dynamically create an INSERT statement in a function
that sometimes receives NULL values.

This is still strange to me.  In Oracle, the same query would not
replace the *entire* string with a NULL, it treats the NULL as a no
value.

I can't find in the documentation where string concatenation of any
string and NULL is NULL.

-Don