SQL> CREATE TABLE T0430 AS SELECT NULL X FROM DUAL;
CREATE TABLE T0430 AS SELECT NULL X FROM DUAL
                             *
ERROR at line 1:
ORA-01723: zero-length columns are not allowed 


Elapsed: 00:00:00.01
SQL> CREATE TABLE T0430 AS SELECT CAST(NULL AS VARCHAR2(1)) X FROM DUAL;

Table created.

Elapsed: 00:00:00.01
SQL> CREATE VIEW V0430 AS SELECT NULL X FROM DUAL;

View created.

Elapsed: 00:00:00.00
SQL> DESC T0430
 Name                                                                                                              Null?    Type
 ----------------------------------------------------------------------------------------------------------------- -------- ----------------------------------------------------------------------------
 X                                                                                                                          VARCHAR2(1)

SQL> DESC V0430
 Name                                                                                                              Null?    Type
 ----------------------------------------------------------------------------------------------------------------- -------- ----------------------------------------------------------------------------
 X                                                                                                                          VARCHAR2

SQL> SELECT column_name, data_type, data_length
  2  FROM user_tab_columns
  3  WHERE table_name='V0430';

COLUMN_NAME                    DATA_TYPE                                                                                                  DATA_LENGTH                                                   
------------------------------ ---------------------------------------------------------------------------------------------------------- -----------                                                   
X                              VARCHAR2                                                                                                             0                                                   

Elapsed: 00:00:00.00
SQL> SPOOL OFF


SQL> DROP TABLE T0430;

Table dropped.

Elapsed: 00:00:00.68
SQL> CREATE TABLE T0430( X VARCHAR2(0));
CREATE TABLE T0430( X VARCHAR2(0))
                                *
ERROR at line 1:
ORA-01723: zero-length columns are not allowed 


Elapsed: 00:00:00.00
SQL> CREATE TABLE T0430 AS SELECT CAST(NULL AS VARCHAR2(1)) X FROM DUAL;

Table created.

SQL> set linesize 80
SQL> CREATE TABLE T0430 AS SELECT NULL X FROM DUAL;
CREATE TABLE T0430 AS SELECT NULL X FROM DUAL
                             *
ERROR at line 1:
ORA-01723: zero-length columns are not allowed 


Elapsed: 00:00:00.01
SQL> CREATE TABLE T0430 AS SELECT CAST(NULL AS VARCHAR2(1)) X FROM DUAL;

Table created.

Elapsed: 00:00:00.01
SQL> CREATE VIEW V0430 AS SELECT NULL X FROM DUAL;

View created.

Elapsed: 00:00:00.01
SQL> COLUMN column_name FORMAT a20
SQL> COLUMN data_type FORMAT a20
SQL> column data_length format 99999
SQL> SELECT column_name, data_type, data_length
  2      FROM user_tab_columns
  3      WHERE table_name='V0430';

COLUMN_NAME          DATA_TYPE            DATA_LENGTH                           
-------------------- -------------------- -----------                           
X                    VARCHAR2                       0                           

Elapsed: 00:00:00.01
SQL> SELECT column_name, data_type, data_length
  2      FROM user_tab_columns
  3      WHERE table_name='T0430';

COLUMN_NAME          DATA_TYPE            DATA_LENGTH                           
-------------------- -------------------- -----------                           
X                    VARCHAR2                       1                           

Elapsed: 00:00:00.04
SQL> DROP TABLE T0430
  2  /

Table dropped.

Elapsed: 00:00:00.01
SQL> CREATE TABLE T0430( X VARCHAR2(0));
CREATE TABLE T0430( X VARCHAR2(0))
                                *
ERROR at line 1:
ORA-01723: zero-length columns are not allowed 


Elapsed: 00:00:00.00
SQL> CREATE TABLE T0430 AS SELECT CAST(NULL AS VARCHAR2(1)) X FROM DUAL;

Table created.

Elapsed: 00:00:00.03
SQL> SPOOL OFF

SQL> CREATE TABLE T0430 AS SELECT CAST(NULL AS VARCHAR2(1)) X FROM DUAL;