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Re: NULLS and string concatenation

From: Don Drake <dondrake(at)gmail(dot)com>
To: Richard Huxton <dev(at)archonet(dot)com>
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: NULLS and string concatenation
Date: 2004-11-19 18:40:02
Message-ID: (view raw or whole thread)
Lists: pgsql-sql
On Fri, 19 Nov 2004 17:48:34 +0000, Richard Huxton <dev(at)archonet(dot)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

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


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