Iam new in using parameters

for example I have ib_query like this

select *
from customer
where type = :paramtype

then i will be having a onclick event for a button like this

ib_query.parambyname('paramtype').asstring = 'ABC';
ib_query.refresh;


so what happen is all the records with type = 'ABC' will be show

what if I want all records to be shown? What should I do? Is there
something like this

ib_query.parambyname('paramtype').asstring = *

or

ib_query.parambyname('paramtype').asstring = any;


thanks