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Re: NULLS and string concatenation

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

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