alter system set nls_length_semantics='CHAR' scope=both;

begin
 for i in (select ('ALTER TABLE '|| C.owner || '.' || C.table_name|| ' modify (' || C.column_name || ' '|| C.data_type || '(' || C.char_length|| ' CHAR))') as Q from all_tab_columns C, all_tables T where  C.owner = T.owner and C.table_name = T.table_name and C.char_used = 'B' and C.table_name not in (select table_name from all_external_tables) and C.data_type in ('VARCHAR2', 'CHAR') ) LOOP
   BEGIN
	execute immediate i."Q"||' ';
   EXCEPTION 
        WHEN OTHERS 
        THEN dbms_output.put_line(SQLCODE||i."Q"||' ');
   END;	
 end loop;
end;
/

 EXECUTE UTL_RECOMP.RECOMP_PARALLEL(4);