select to_char(to_date('2006', 'yyyy'), 'yyyymmdd hh24:mi:ss') from dual;

CREATE OR REPLACE FUNCTION TRY_TO_NUMBER 
(p_val in varchar2)
RETURN NUMBER AS 
  v_number number;
BEGIN
  begin 
    v_number := to_number(p_val);  
    exception
      when VALUE_ERROR then     
      v_number := 0;
   end;
   return v_number;
END TRY_TO_NUMBER;