[Qgis-user] Problem filtering table on columns with NULL values

[chris hermansen]

Bernd and list,

On Thu, Oct 15, 2020 at 5:18 AM Bernd Vogelgesang <bernd.vogelgesang at gmx.de>
wrote:

> Hi,
>
> just hit a problem when working with a table from an .ods file.
>
> To work with the data, I have to exclude some values from a field, where
> some entries also have NULL values.
>
> When I now filter on the value I do not need ("field" != 'xyz'), also
> the rows with  NULL values in that field are filtered out, which is not
> what I want.
>

In databases that support NULL values it's customary to use "IS NULL"
rather than "= NULL".   The rationale is that a boolean expression
involving NULL values can't be true nor false since the meaning of NULL is
"unknown".


> As I do not want to "invent" data for those rows just to make it work, I
> wonder if this is a bug or if there is a workaround for this problem.
>

I just tried this with the QGIS select calculator (IS NULL) and it seems to
work fine there.




-- 
Chris Hermansen · clhermansen "at" gmail "dot" com

C'est ma façon de parler.
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