Items not included SharePoint search results if a property missing

Question

I use an MSSQLFT query to poll Sharepoint's search through Search.asxm web service.

The query goes like this:

SELECT PreferredName, Department, AccountName, MobilePhone, WorkPhone
       Title, JobTitle, OfficeNumber
FROM SCOPE()
WHERE 
     "scope"="People" AND JobTitle="Something"
ORDER BY
       Department, OfficeNumber

Some people do not have Depmartment attribute set and hence are not included in search results.
If I remove the "Department" part from "Order by" clause, everything works fine. Is there a way to provide "default value" for such missing property so that these people would still get included?