[MapServer-users] NULL-EXPRESSION

[Björn Danielsson]

This works for me.
Try this:

Create two layers with the same name and group.

Layer 1 ( takes care of values 2000 and 2100) :
LAYER
    NAME  "A"
   GROUP "A"
   .....

   PROCESSING 'NATIVE_FILTER=gst IS NOT NULL'

  CLASS for 2000
....

  CLASS for 2100
....

END

Layer 2 ( value = NULL ) ❤️

LAYER
   NAME  "A"
   GROUP "A"
   ....

  PROCESSING 'NATIVE_FILTER=gst IS NULL'

 CLASS for NULL
....

END


________________________________
Från: MapServer-users <mapserver-users-bounces at lists.osgeo.org> för Seth G via MapServer-users <mapserver-users at lists.osgeo.org>
Skickat: den 28 mars 2025 10:43
Till: angelique.kroisl at stadt-koeln.de <angelique.kroisl at stadt-koeln.de>; MapServer Users <mapserver-users at lists.osgeo.org>
Ämne: Re: [MapServer-users] NULL-EXPRESSION

Hi,

Unfortunately, MapServer doesn't have a NULL type.
The workaround is to create a database view or query that will set the NULL to a numeric value of your choosing, e.g. -1 and then use that value in the CLASS expressions.

Seth

--
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On Fri, Mar 28, 2025, at 8:55 AM, Angelique Kroisl via MapServer-users wrote:

Hello,

I'm trying to create a class using the class item "gst."

The attribute in the database can only have three values (2000, 2100, and <NULL>).

Unfortunately, I can't create the NULL EXPRESSION.



I've already tried the following:

EXPRESSION IS NULL



EXPRESSION "<NULL>"



EXPRESSION <NULL>



EXPRESSION EMPTY



What is the correct syntax for this?


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