From: Herouth Maoz <herouth@tippcom.co.il>
Organization: TippCom
To: pgsql-sql@postgresql.org
Subject: Re: Differentiate Between Zero-Length String and NULLColumn  Values
Date: Tue, 30 Jan 2007 16:37:43 +0200
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Andrew Sullivan Wrote:

> On Tue, Jan 30, 2007 at 02:38:07PM +0100, Bart Degryse wrote:
> > Andrew, I think you're wrong stating that Oracle would interpret
> > NULL and empty string as equal. The Oracle databases I use (8, 9
> > and 10) certainly make a distiction between both values. Maybe
> > earlier versions did so, that I don't know.
>
> Hmm.  Well, I'm not an Oracle guy, so I don't really know.  All I
> know is that we occasionally get people coming from Oracle who are
> surprised by this difference.  What I've been _told_ is that '' and
> NULL are under some circumstances (maybe integers?) the same thing,
> whereas of course ' ' and NULL are not.  But since I'm not an Oracle
> user, people should feel free to ignore me :)

Sybase does something like that... In sybase, null and empty string are the 
same. However, to avoid the equality ''=NULL, they actually interpret '' as a 
single space. So if you do something like SELECT 'A'+''+'C' (concatenation is 
+ in sybase), it results in 'A C'. Null is a "real" empty string in that its 
length is zero, and if you insert a trim('') into a column, it will treat it 
as NULL.

Herouth