Using QGIS 2.2, I would like to create a rule-based filter whereby you add 2 columns together and you get a certain colour as a result. However, some fields in Column_1 may be NULL and those exact same fields may have values in Column_2 and vice-versa.
Is there an expression to add the 2 columns whilst ignoring the NULL values or atleast treating them as zero?
The following is the logic I am trying to achieve:
1 + 2 = 3
1 + NULL = 1
NULL + 2 = 2
Additional info: The data from the columns are JOINED from other layers, I do not want to create any new columns as I am wanting the colours of layers to dynamically change when the user adds or removes the JOINED layers.