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<p>Out of curiosity, what happens if you execute the same query via
the Virtual layer dialog or through the DB Manager? This would
highlight any differences between QGIS Expression SQL and a DBMS (the
SQLite engine). </p>
<div class="moz-cite-prefix">On 15/07/2021 08:17, Andrew Hughes
wrote:<br>
</div>
<blockquote type="cite" cite="mid:CAMvYC1UA_yHBQhbEppm5iCWWduzA2Zq5Ke4Ks4pVFU41sRRk1Q@mail.gmail.com">
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<div dir="ltr">Thanks Marco,
<div><br>
</div>
<div>You've answered my question, so thank you. For reference,
I've never see this in any sql rmdbs.<br>
</div>
<div><br>
</div>
<div>Some examples my help the community, hopefully I will be
able to contribute sooner or later.</div>
<div><br>
</div>
<div>Thanks again!</div>
<div>Andrew</div>
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<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, 7 Jul 2021 at 17:43,
GMAIL <<a href="mailto:casalbonim@gmail.com" moz-do-not-send="true">casalbonim@gmail.com</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
This is how sql works.<br>
You want to apply a function to one column, and the column
you are <br>
comparing must have a value.<br>
Consider this: tag_service != 'xxx' or null != 'xxx'. Null
can't be <br>
equal or unequal to any value. Even null = null or null !=
null returns <br>
false<br>
<br>
hth<br>
marco<br>
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<pre class="moz-signature" cols="72">--
Andy Harfoot
Skype: gdi_ajph
Teams: <a class="moz-txt-link-abbreviated" href="mailto:ajph@soton.ac.uk">ajph@soton.ac.uk</a>
GeoData Institute
University of Southampton
Southampton
SO17 1BJ
<a class="moz-txt-link-abbreviated" href="http://www.geodata.soton.ac.uk">www.geodata.soton.ac.uk</a></pre>
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