Message-ID: <419E31F2.4060104@archonet.com>
Date: Fri, 19 Nov 2004 17:48:34 +0000
From: Richard Huxton <dev@archonet.com>
User-Agent: Mozilla Thunderbird 0.9 (X11/20041103)
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To: Don Drake <dondrake@gmail.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: NULLS and string concatenation
References: <6c21003b0411190912630d4afe@mail.gmail.com>
In-Reply-To: <6c21003b0411190912630d4afe@mail.gmail.com>
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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 was able to work around the problem by using COALESCE (and casting
> variables since it wants the same data types passed to it).

That's the correct procedure (although ask yourself if you should have 
nulls rather than just empty strings).

-- 
   Richard Huxton
   Archonet Ltd