35
votes
Accepted
What is the difference between != NULL and IS NOT NULL in QGIS filter expressions?
Disclaimer: Because the syntax for filtering in QGIS works with SQL, I'm assuming here that SQL rules apply. I'm not completely sure if that's entirely correct, but it seems logical and it does ...
- 2,295
25
votes
Accepted
Concatenating labels in QGIS
This is because concatenate() is an aggregate function (i.e. it looks up the values for that attribute across all features), so when you try for example concatenate("GROUP") you'll still end ...
- 10.1k
24
votes
What is the difference between != NULL and IS NOT NULL in QGIS filter expressions?
NULL is not a value, therefore it cannot equal = or not equal != anything. It is not the same as zero 0 which is a value.
A NULL indicates that no value has been recorded in the cell you are looking ...
- 29.5k
23
votes
Replacing all null values from attribute table with zeros in QGIS
You can do this directly in the field calculator:
Open the field calculator
Check the “Update Existing Field” box
Select the field you want to work on
Enter the following expression in the expression ...
- 749
18
votes
Accepted
Importing NULL in PyQGIS
The NULL class is defined in qgis.core:
import qgis.core
if f["SAMPLE"] == qgis.core.NULL:
...
Normally you should be able to do a normal is None check however due to tool we use to ...
- 34.6k
12
votes
Accepted
Selecting NULL or date values by Expression in QGIS
I don't know why, but this worked:
to_date(field) IS NULL or field > '2020-01-01'
Type of "field" is date.
- 74.7k
11
votes
Accepted
Why blank values in attribute table don't work as NULL in QGIS?
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 ...
- 27.5k
10
votes
Accepted
QGIS: Delete all records/rows with NULL values
In the attribute table, choose Select by Expression and write "FIELD_NAME" IS null (replace FIELD_NAME with your actual field names, of course). Click "Select Features", then simply delete the ...
- 1,284
10
votes
Accepted
Referring to Null value with ArcPy Expressions?
Your problem is that in Python 2 None is less than everything.
>>> None < 20
True
>>> None < numpy.nan
True
>>> None < float('-inf')
True
>>> None < '...
- 64k
9
votes
Batch removing null geometries
Removing null geometries from just a few layers
Use the "select by expression" button to select features with null geometries. The "select by expression" button is found by clicking the arrow next to ...
- 24.3k
9
votes
Accepted
Handling null inside .map in Google Earth Engine
There is not a great way to skip an image in the map function. However, you can use the ee.Algorithms.If function to control what happens when null is encountered. In your case, if all pixels in the ...
- 6,036
8
votes
Changing 0 to NULL in QGIS Attribute table
select all your '0' rows -> Go to 'Select by expression' and select all rows where attribute = 0
Go to 'Field calculator' and check 'Update existing field', 'Only update selected features' and select ...
- 1,066
8
votes
Accepted
Nullifying the whole row in data attribute table at once in QGIS
You can do it with a few lines in the Python console. As with any script which permanently edits a layer in place (this one does), I recommend making a backup copy of your file first. One other caveat-...
- 20.2k
7
votes
Accepted
Allowing NULL value in field's value map in QGIS?
Implemented the value maps of Edit Widget Property on one of Reservoirs layer. I have an attribute with type of reservoir (this water body could be Reservoir, Dam, Anicut or even null) and I had no ...
7
votes
Accepted
QGIS constraint not null depending on another field value
On field B, for constraints use this expression:
case
when "field_A" = 'foo' then not (field_B is NULL)
when "field_A" <> 'foo' then field_B is NULL or field_B is ...
- 63.1k
7
votes
Deleting contents of all entries in field in QGIS Attribute table
You could use the field calculator to update the field to '', aka an empty field. Beware that this is not NULL.
As J.R pointed out in the comments, null provides a NULL-value in your field.
- 15.5k
6
votes
Accepted
Python script for filling <Null> values with previous value in one field
You can do this directly within the CalculateField tool; use the following code block:
prevval = None
def calcowner(ownerval):
global prevval
val = prevval if ownerval is None else ownerval
...
- 6,221
6
votes
Accepted
Calculate all 'Null' integer fields to '0'?
You can do this for many fields with some Python. This is a stand alone example, but it'd be easy to write this into a script/Python toolbox. Or you could embed this into another loop and do this on a ...
- 6,221
6
votes
Accepted
Can a SHAPE field be non-nullable?
Yes and No. As @whyzar has answered, you can change the Allow NULL values property on the SHAPE field.
However, this will not stop features being added without geometry!
To emphasise the point at ...
- 29.5k
6
votes
Accepted
Representing NULL data for a numeric field in ArcGIS (symbology)
Create an exclusion in your symbol classification. In your Layer Properties > Symbology tab, click Classify. In the Classification dialog click Exclusion:
On the Query tab, add an exclusion for ...
- 29.5k
6
votes
Use gdal to set multiband raster values to no data
The syntax is documented on the manual page https://www.gdal.org/gdalwarp.html as
If more than one value is supplied all values should be quoted to keep
them together as a single operating system ...
- 62k
6
votes
Hiding NULL text in attributes using QGIS?
From Settings -> Options -> Data Sources -> Delete NULL text:
Before deletion:
After deletion:
- 40.3k
6
votes
Changing 0 to NULL in QGIS Attribute table
After selecting the layer, use this script in the QGIS's Python Editor (Ctrl+Alt+P):
from qgis.utils import iface
layer = iface.activeLayer()
idx = range(layer.fields().count())
layer.startEditing()...
- 74.7k
6
votes
Accepted
Fill combobox with NULL values in PyQGIS
'NULL' is not different from any string. Instead, you should use NULL. Remove apostrophes. NULL is automatically imported in QGIS. Outside QGIS you need to import NULL. It is a PyQGIS variant, not ...
- 74.7k
6
votes
Accepted
Concatenate multiple fields where some contain null values (QGIS)
First possibility: use concat and replace double commas where you have empty entries:
replace( concat (field_a,', ',field_b,', ',field_c), ', ,', ',')
Second possibility: use arrays to concatenate, ...
- 63.1k
6
votes
Accepted
Date coming through as NULL when data type is set to "date" in csv/t
Your date is not a date. It is a string representing a date. A date is in format yyyy-MM-dd. You can convert it to a date once you loaded your data as string, e.g. by adding a virtual field via field ...
- 32.6k
6
votes
Deleting contents of all entries in field in QGIS Attribute table
After selecting the layer, use this script in the Python Editor of QGIS:
layer = iface.activeLayer()
# make a dictionary for indexed NULL value
null_attr = {i: NULL for i in range(layer.fields()....
- 74.7k
6
votes
Deleting NULL geometries and duplicate nodes from table using PostGIS
This requires a procedural execution of dynamic SQL - best applied with a DO block.
Since we are only looking at modifying columns of type GEOMETRY, we can identify the respective relations easily ...
- 28.8k
5
votes
Accepted
Using Null values in Field Calculator
You can create a list and check if your value exists in that list. Place your possible Null/empty/spaced values into that list and check them all at once.
def findnulls(fieldname):
if rec_a in [...
- 29.5k
5
votes
Accepted
ArcMap Field Calculator Remove Null values
Im sure this is Python and not VB script. By putting the 0 in speech marks, you are trying to say that 0 is a string, when its not. As added by Martin, please select the Python Parser instead of the ...
- 2,281
Only top scored, non community-wiki answers of a minimum length are eligible