BEGIN
  FOR l_rec IN (SELECT 1
                  FROM user_tables
                 WHERE table_name = 'GTT_DIR_LIST') LOOP
    EXECUTE IMMEDIATE 'DROP TABLE gtt_dir_list';
  END LOOP;
END;
/
create GLOBAL temporary table gtt_dir_list
(filename varchar2(255) ,filelength NUMBER, filetype VARCHAR2(255), filemodified DATE)
on commit delete rows
/