Search fields join

Summary

Is it possible to use two different search fields and get results for both?

Content

We are using two fields for more or less the same thing, let's call it 'mission_old' and 'mission_new'. For none of the requisitions both are filled in, a requisition has either 'mission_old' or 'mission_new' filled in. Our users would like to use both fields in their search in order to get all the requisitions in their view on either mission filled in in the search field. Is there a way to make this work? At the moment the search then looks for both values in a requisition and that is never the case.