Rule based display labels, show different value with first is null

Question

I am attempting to create a mapping system for navigation at my small fire department using QGIS and a GPS. I am attempting to show spaces in a trailer park or apartment building instead of the street address. So instead of the label 1234, 1234, 1234, 1234, over and over, it would read (space: 1, 2, 3, 4, 5) Some of these are very close together so I was hoping that if value "space Number" is present then value "address" is absent. Also, if there is no space number it would just read the address.

I attempted the "ADDRESS || '\n' || SPACE" and when I do so it only shows the labels that have both values. I just want one or the other, how could I write that expression.

Answer 1

Instead of putting the whole condition into one expression, you can also create two, to handle the two cases separately. See the following screenshot for details:

By using this rules, the value from the column "space" is used as a label, if a value exists. Otherwise it shows the "address" value of the feature.