Are you getting an 'unknowed column' error? If not then the query is probably executing correctly but does not have a proper value for the column alias you created.
When you test this query out can you reference your calculated columns and see the correct value for them? This will be the first step in getting it to work. Once that is done you should be able to reference the same name in the DA Search server behavior. If you have any further problems with it post back with the entire search page and I can add some debug code to print out the query that is being executed to get a better idea for how this is being handled.