Creating field which is a value dependent on other fields

I think that the way I could do this is by having a conditional value. Basically this is what I will need to do...1. have a field called Customer which will be by default 0, if there is a customer assigned to this work item, then set to 1.2. Create a query which will sort first by the field Customer, then by Priority and then by severity.This way, developers could come in in the morning and see their highest priority bugs (i.e. those associated with a customer) and do their work accordingly.Does anyone know how I can do the first part of this? Thanks in advance for your help.