#define in SQL?

I've looked in some SQL books and online, but can't seem to find what
I'm looking for ...

The "copy" statement requires absolute paths to indicate file names.
Since these can be quite long, I would like a way -- similar to the C
pre-processor's "#define" -- to define a symbol in the beginning of my
SQL code that can be referenced later.

In a C program I'd write:

#define EXPORTFILE "/home/khj/tmp/pgsql.export"

Can something similar be done in SQL?

Thanks,

-Prof Kenneth H Jacker khj(at)cs(dot)appstate(dot)edu
-Computer Science Dept www.cs.appstate.edu/~khj
-Appalachian State Univ
-Boone, NC 28608 USA