Filling column with values at certain condition in QGIS

How do I add values to an attribute table in QGIS?

Right click the layer in the Layers Panel then click the Open Attribute Table menu option. Click the Toggle Editing Mode button. Click the New Field button. Input the field’s Name, Type, and Length, then click the OK button.

How do I filter attributes in QGIS?

Filtering

1. In the Layers Panel, double-click on the layer you wish to filter. The Layer Properties window will open.
2. Click on the General tab.
3. Go to the Query Builder at the bottom right and click on it. You can now enter a Query.
4. Click on OK and then on OK again.

How do I Autonumber a field in QGIS?

Autonumber new features

1. Open the “Properties” of your layer and go to the tab “Attributes Form”.
2. In “Available Widgets” select the field you want to add autonumber to. In this example that is “nummering”.
3. Uncheck the checkbox “Editable” in “General”.
4. In the box “Default value” write: maximum(“nummering”)+1.
5. Click OK.