order by decode( p_method, 'asc', 1, -1 ) * id


OR, you would have to use a ref cursor:


if ( p_method = 'desc' )
then
open c_m for select id,qty
from t_stock
where qty>0
order by id DESC;
else
open c_m for select id,qty
from t_stock
where qty>0
order by id ASC;
end if;

But since I cannot see an index being used to present the data "sorted" anyway (the range scan on qty>0 will not have id sorted if the index is on (qty,id) so it'll sort at the end anyway and if the index is on id,qty -- it will have to search the entire index.... so thats not a good solution either) the decode method should be "just fine"