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I am new to QGIS and am having, what I expect to be, an easy issue. I am working with a multi-polygon shapefile of taxable property parcels in QGIS 3.16.

All it is I am trying to do is select all features whose "FieldA" is empty (or "Null")

In the expression field I have tried: "FieldA" = 0; or "FieldA" = NULL

Neither of these work obviously and I am at a bit of an impasse.

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    FieldA IS NULL is the SQL standard, though shapefiles don't support NULLs, so if it's a text field, then FieldA = '' – Vince Jan 6 at 20:13
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Use "FieldA" is NULL to select the features whose FieldA is NULL. If the field type is string, then you also should use "FieldA" = '' to select the features whose FieldA is empty. In QGIS, being empty doesn't mean being NULL.

And use "FieldA" is NULL or "FieldA" = '' to select all NULL and empty.

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