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It was at least 5 years since I struggled with this.</div>
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The map should show a gradient with values like 0, 1-19, 20-39 and so on.</div>
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A lot of classes, and I found out that records with a column with null value were returned as value 0 and therefore ended up in</div>
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class expression ( x = [0]) together with real values = 0.</div>
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That is why I created two layers with the same name as I described in my first mail.</div>
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However, if you have no need to differ between 0 and null I think you can either have a class with expression ( x=[0]), or perhaps as Richard G suggested</div>
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no expression at all, which would be simplest.</div>
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Björn D</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>Från:</b> MapServer-users <mapserver-users-bounces@lists.osgeo.org> för Richard Greenwood via MapServer-users <mapserver-users@lists.osgeo.org><br>
<b>Skickat:</b> den 28 mars 2025 16:19<br>
<b>Kopia:</b> angelique.kroisl@stadt-koeln.de <angelique.kroisl@stadt-koeln.de>; MapServer Users <mapserver-users@lists.osgeo.org><br>
<b>Ämne:</b> Re: [MapServer-users] NULL-EXPRESSION</font>
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<div dir="ltr">Have you tried making your CLASS for NULLs the last of the three classes and with no EXPRESSION? The first two classes would pick up 2000 and 2100 and then anything not matching would be in the third class. This works in most cases but I haven't
tried it with NULLs.</div>
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<div>Rich</div>
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<div dir="ltr" class="x_gmail_attr">On Fri, Mar 28, 2025 at 4:36 AM Björn Danielsson via MapServer-users <<a href="mailto:mapserver-users@lists.osgeo.org">mapserver-users@lists.osgeo.org</a>> wrote:<br>
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This works for me.</div>
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Try this:</div>
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Create two layers with the same name and group.</div>
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Layer 1 ( takes care of values 2000 and 2100) :</div>
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LAYER</div>
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NAME "A"</div>
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GROUP "A"</div>
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.....</div>
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PROCESSING 'NATIVE_FILTER=gst IS NOT NULL'</div>
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CLASS for 2000</div>
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....</div>
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CLASS for 2100</div>
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....</div>
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END</div>
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Layer 2 ( value = NULL ) ❤️</div>
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LAYER</div>
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NAME "A"</div>
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GROUP "A"</div>
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....</div>
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PROCESSING 'NATIVE_FILTER=gst IS NULL'</div>
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CLASS for NULL</div>
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....</div>
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END</div>
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<div id="x_m_-6977349107554290354divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>Från:</b> MapServer-users <<a href="mailto:mapserver-users-bounces@lists.osgeo.org" target="_blank">mapserver-users-bounces@lists.osgeo.org</a>>
för Seth G via MapServer-users <<a href="mailto:mapserver-users@lists.osgeo.org" target="_blank">mapserver-users@lists.osgeo.org</a>><br>
<b>Skickat:</b> den 28 mars 2025 10:43<br>
<b>Till:</b> <a href="mailto:angelique.kroisl@stadt-koeln.de" target="_blank">angelique.kroisl@stadt-koeln.de</a> <<a href="mailto:angelique.kroisl@stadt-koeln.de" target="_blank">angelique.kroisl@stadt-koeln.de</a>>; MapServer Users <<a href="mailto:mapserver-users@lists.osgeo.org" target="_blank">mapserver-users@lists.osgeo.org</a>><br>
<b>Ämne:</b> Re: [MapServer-users] NULL-EXPRESSION</font>
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<div>
<div>Hi,<br>
</div>
<div><br>
</div>
<div>Unfortunately, MapServer doesn't have a NULL type.<br>
</div>
<div>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.<br>
</div>
<div><br>
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<div>Seth</div>
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<div>--<br>
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<div>web:<a href="https://geographika.net" target="_blank">https://geographika.net</a> & <a href="https://mapserverstudio.net" target="_blank">https://mapserverstudio.net</a><br>
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<div>On Fri, Mar 28, 2025, at 8:55 AM, Angelique Kroisl via MapServer-users wrote:<br>
</div>
<blockquote type="cite" id="x_m_-6977349107554290354x_qt">
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<p>Hello,<br>
</p>
<p>I'm trying to create a class using the class item "gst."<br>
</p>
<p>The attribute in the database can only have three values (2000, 2100, and <NULL>).<br>
</p>
<p>Unfortunately, I can't create the NULL EXPRESSION.<br>
</p>
<p> <br>
</p>
<p>I've already tried the following:<br>
</p>
<p>EXPRESSION IS NULL<br>
</p>
<p> <br>
</p>
<p>EXPRESSION "<NULL>"<br>
</p>
<p> <br>
</p>
<p>EXPRESSION <NULL><br>
</p>
<p> <br>
</p>
<p>EXPRESSION EMPTY<br>
</p>
<p> <br>
</p>
<p>What is the correct syntax for this?<br>
</p>
</div>
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</p>
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<span class="x_gmail_signature_prefix">-- </span><br>
<div dir="ltr" class="x_gmail_signature">
<div dir="ltr">Richard W. Greenwood<br>
<a href="http://www.greenwoodmap.com" target="_blank">www.greenwoodmap.com</a></div>
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