Ah, suddenly it all becomes clear :)
Thanks all

regards mattc

On Thu, 2003-10-09 at 11:20, Martijn Tonies wrote:
> Hi Matt,
>
>
> > where memo <>'DIS' or memo is null?
> > or another solution
> > SELECT col1, col2, col3 where memo <>'DIS'
> > union
> > SELECT col1, col2, col3 where memo is null
>
> The reason for this, is that SQL knows two states for a value:
> NULL and NOT NULL
> or, translated to normal human language:
> Unknown and Known
> Empty and Filled
>
> As you might have guessed by now -
>
> You can't do a thing like:
>
> Unknown value <> 'DIS'
>
> but you need to explicitly ask for either values that are known
> and different than DIS or unknown values.
>
> MEMO <> 'DIS' OR MEMO IS NULL
>
>
> With regards,
>
> Martijn Tonies
> Database Workbench - developer tool for InterBase, Firebird & MS SQL Server.
> Upscene Productions
> http://www.upscene.com
>
>
>
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>


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