How to show labels for all polygons in a layer, even with 'NULL' values?

Question

I have a polygon layer which contain information on property name, number of trees within the polygon, average height, and min- and max height values.

My problem is, I want to label each polygon with property name, number of trees, etc. I got that part to work, the labels looks the way I want them. But, I have a number of properties which doesn't contain any trees. When making labels, the properties without tree doesn't get labelled at all?

I would like labels on the properties without trees to show just the names of the properties. Is this possible in QGIS 2.2?

Answer 1

There's two ways you could do this. One is to wrap your field that contains some nulls by the 'coalesce' function:

Coalesce("tree_field_name", '0 trees')

This would use the value in tree_field_name if it's non null, otherwise it will use the string '0 trees' (pay attention to the use of " and ').

The alternative is to use a "case when" function:

Case when "tree_field_name" is null then '0 trees' else "tree_field_name" end

This will have the same result.

Answer 2

I came up with a solution to my problem.

I saved all the properties without trees in a new shapefile. Then I labelled the new layer with property names. So now i have two layers, one with the polygons of all the properties and labels on the ones with trees and one layer with only the labels of the properties without trees. When I show them together I get the result I wanted.

If possible, I still really want to learn how do this without creating a new layer.