-- SESSION 1 
drop table tt purge ;
create table tt nologging as select user usr, sysdate sd from dual ;
select * from tt ;

USR                            SD
------------------------------ ----------
HR                             28/01/2007

insert into tt values ('TONGUC', sysdate-1) ;

1 row created.

-- SESSION 2
select * from tt ;

USR                            SD
------------------------------ ----------
HR                             28/01/2007		!! attention session 2 can not see the new inserted row since it is not yet commited by session 1 !!

-- SESSION 1 
create table tt nologging as select user usr, sysdate sd from dual ;
create table tt nologging as select user usr, sysdate sd from dual
             *
ERROR at line 1:
ORA-00955: name is already used by an existing object

-- SESSION 2
select * from tt ;

USR                            SD
------------------------------ ----------
HR                             28/01/2007
TONGUC                         27/01/2007		!! attention DDL failed, we didnt commit but this row can be seen from session 2 which means it doesnt matter you rollback in session 1 this row will remain in the table !!