Why blank values in attribute table don't work as NULL in QGIS?

Question

In QGIS 3.4 I have a layer generated from the QuickOSM Plugin with various pieces of OSM data.

For lines 17-19 which do not have a value in the "name" attribute, I don't know why null isn't showing up. I would like to select all the rows that have the name value empty. I tried using name is null, but that did not select anything. In settings, I have the option selected to say null in any blank values. My only guess is that maybe these values somehow are not empty, but they seem to be blank and I have tried writing something and then deleting it.

So what I would like to know is how I would select all rows of the table that don't have a value in the name column. Also, if someone could explain why NULL isn't showing up in the values that would be helpful.

Answer 1

NULL is not equal to an empty string. NULL is by definition an "unknown value" of which we cannot assume anything. Whereas an empty string is a string without contents. You can test for NULL by using "column_name" IS NULL and for an empty string by using "column_name" = ''

Apparently in your data there are no NULL values but only empty strings.

What you can do is

• Replace every empty string with NULL by using the field calculator with the expression NULLIF("name", '') (QGIS >= 3.6 required)
• Use "name"= '' as selection criteria