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).
On 15/07/2021 08:17, Andrew Hughes wrote:
*CAUTION:* This e-mail originated outside the University of Southampton.
Thanks Marco,
You've answered my question, so thank you. For reference, I've never
see this in any sql rmdbs.
Some examples my help the community, hopefully I will be able to
contribute sooner or later.
Thanks again!
Andrew
On Wed, 7 Jul 2021 at 17:43, GMAIL <[email protected]
<mailto:[email protected]>> wrote:
This is how sql works.
You want to apply a function to one column, and the column you are
comparing must have a value.
Consider this: tag_service != 'xxx' or null != 'xxx'. Null can't be
equal or unequal to any value. Even null = null or null != null
returns
false
hth
marco
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Andy Harfoot
Skype: gdi_ajph
Teams: [email protected]
GeoData Institute
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SO17 1BJ
www.geodata.soton.ac.uk
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