SQL> select 'x' from dual;

'
-
x

SQL>

select bookno_seq.nextval into :books.sr_no from SYS.dual;

SQL> col owner format a15
SQL> col synonym_name format a15
SQL> col table_owner format a15
SQL> col table_name format a15
SQL> col db_link format a10
SQL>
SQL> select * from all_synonyms where synonym_name = 'DUAL';

OWNER           SYNONYM_NAME    TABLE_OWNER     TABLE_NAME      DB_LINK
--------------- --------------- --------------- --------------- ----------
PUBLIC          DUAL            SYS             DUAL

SQL>

SQL> create public synonym dual for sys.dual;