How to best implement ORDER BY of a query when the field by which to
order, is given as stored procedure input parameter?
for example a typical product list where could be ordered by Name, Price
etc fields depending on what user clicks.

I tried to include it into query:

for
select f1, f2 from t1
order by :order_by_field
into :p1, :p2

I am not getting any errors, but it doesn't order the list. how to do it
better?
thanks.