conditional query?

I have a table called a "profile" that has company addresses as well
as individual contact information. Simpifying:

id (the primary key)
parentId (any profile can have a parent ie, contact parent is a company)
address (for this example, will just have one piece of the address)
useParentAddress

If "useParentAddress"=="Y", that means that the parent address of this
person should really be used for mailings. If == "N" then the address
with that profile is the right one to use.

Is there any way to do a single select to get a single "address" back
that is the right one depending on the value of "useParentAddress"
field?

Also want to make this sql as portable as possible.

Will appreciate any ideas.