create or replace function STUFF(p_expr varchar2,
                                 p_start integer,
                                 p_length integer,
                                 p_stuff varchar2)
return varchar2
is
begin
	return case
		when p_start is not null 
			and p_length is not null 
			and p_start > 0 
			and p_start <= length(p_expr) 
		then
			substr(p_expr,1,nvl(p_start,0) - 1)||p_stuff||substr(p_expr,nvl(p_start,0) + nvl(p_length,0))
		else null
	end;
end;