DECODE or CASE STATEMENT for PARAMETER in WHERE CLAUSE
I don't have a database on hand to test this but can't you do something like this:

and SPC.CHARACTERISTIC in ('ARLFT','MINE')
and SPC.CHARACTERISTIC in ('&amp;industry')


With both of those predicates present you will default to both values if you enter '%' but be restricted to just one if you enter either 'MINE' or 'ARLFT'