database field "pointer"

    I was wondering is there is a good method to make a database field a
pointer, similar to C. Here is an example I made up of why this could be
useful:
    Suppose I have a table 'coworkers' with 2 email address fields: work_email
and home_email. It would be useful to have another field that was something
like 'preferered_email' that pointed to one or the other. Then, updates would
only need to happen once, and it would be easy to change back and forth.
    Tell me if there is some better, more sensible method to accomplish this
task.

Thanks,
    Jeff Davis