Combining Columns QGIS Attribute Table

Question

I have two columns in my QGIS attribute table. The first column contains values that aren't contained the second column and vice versa. I would like to add a new field that contains both the values from the first and second column. I thought it might be as simple as "Value 1 + Value 2) but this just gives me Null results. All values are strings.

Value 1| Value 2 | New Column
-------------------------
 Bacon |         | Bacon
 Eggs  |         | Eggs
       | Cheese  | Cheese
       | Ham     | Ham  

Answer 1

Many operators and functions in SQL (and therefore expressions) return NULL if one of the parameters was NULL

The following examples demonstrate the behavior of various operators on a layer with the columns A and B.

"A" + "B"

• NULL + 'text' ➝ NULL
• 'a' + 'b' ➝ 'ab'

"A" || "B"

• NULL || 'text' ➝ NULL
• 'a' || 'b' ➝ 'ab'

CONCAT("A", "B")

• CONCAT(NULL, 'text') ➝ 'text'
• CONCAT('a', 'b') ➝ 'ab'

COALESCE("A", "B")

• COALESCE(NULL, 'text') ➝ 'text'
• COALESCE('a', 'b') ➝ 'a'
• COALESCE('a', NULL) ➝ 'a'
• COALESCE(NULL, NULL, 'Other') ➝ 'Other'

In your case you want to work with either CONCAT or COALESCE depending on the expected behaviour with multiple / no values.

Answer 2

You could use field calculator and follow these steps:

1- Create new field (string)

2- Use "Coalesce" Function

       coalesce(  "Value 1" , "Value 2" , 'value if No data')

Colaesce function returns the first not NULL

Answer 3

Easy way to do a similar thing is by combining column values in a new field e.g. in field calculator (QGIS):

"field_name1" + ',' + "field_name2"

results in new field with combined values from 2 columns/fields separated by a comma. Note that both fields must be of type String, or use to_string("field_name1") + ',' + to_string("field_name2") if they are not.

Answer 4

Select the layer in the layer panel and open the python console and run this snippet:

layer = iface.activeLayer()
layer.startEditing()
fields = layer.pendingFields()
fieldIndex = fields.indexFromName('newColumn')
for feature in layer.getFeatures():
    if feature['value1']:
        layer.changeAttributeValue(feature.id(),fieldIndex,feature['value1'])
    if feature['value2']:
        layer.changeAttributeValue(feature.id(),fieldIndex,feature['value2'])
    if feature['value1'] and feature['value2']:
        layer.changeAttributeValue(feature.id(),fieldIndex,feature['value2'] + ' ' + feature['value2']) # not sure what you want to do here if values found in both value1 and value2 fields
layer.commitChanges()

Answer 5

You also could use the field calculator, add a new field and feed him the following

CASE WHEN "column1" IS NULL
THEN "column2"
ELSE "column1"
END