I think you might want to rethink your design since you end up, as you are no doubt aware, trying to search for the same information in one of 2 places, depending on the number of locations per job. How does that "make the search quicker" compared to doing the obvious: joining the three tables and searching on postal_code in job_locations?
If only the rare job has more than one location, it's possible your design might be faster (anyone know?). If that's the case, you can get your data with a union statement.