CREATE OR REPLACE TRIGGER tri1
AFTER UPDATE
   ON dept
   FOR EACH ROW
   
declare
 pragma AUTONOMOUS_TRANSACTION;
   
BEGIN

   execute immediate 'create table dept_dum as select  * from dept';
     
END;
/

SQL> update dept set deptno=23 where deptno=10;
update dept set deptno=23 where deptno=10
       *
ERROR at line 1:
ORA-01031: insufficient privileges
ORA-06512: at "SCOTT.TRI1", line 6
ORA-04088: error during execution of trigger 'SCOTT.TRI1'

create table as select * from table_name where flag=1

SQL> create or replace trigger tri1
  2     after update
  3     on dept
  4     for each row
  5  declare
  6     pragma autonomous_transaction;
  7  begin
  8     execute immediate 'create table dept_dum as select  * from dept';
  9  end;
 10  /

Trigger created.

SQL>
SQL> update dept
  2     set dname = 'SALES'
  3   where deptno = 30;

1 row updated.

SQL> /
update dept
       *
ERROR at line 1:
ORA-00955: name is already used by an existing object
ORA-06512: at "SCOTT.TRI1", line 4
ORA-04088: error during execution of trigger 'SCOTT.TRI1'


SQL> drop table dept_dum;

Table dropped.

SQL> update dept set dname = dname;
update dept set dname = dname
       *
ERROR at line 1:
ORA-00955: name is already used by an existing object
ORA-06512: at "SCOTT.TRI1", line 4
ORA-04088: error during execution of trigger 'SCOTT.TRI1'


SQL>