SQL> create table ext_emp(ename varchar2(20),age number)
  2  organization external(
  3  type oracle_loader
  4  default directory dir1
  5  access parameters
  6  (fields terminated by ','
  7  )
  8  location('emp.txt')
  9  )
 10  /

Table created.

SQL> desc ext_emp;
 Name                                                  Null?    Type
 ----------------------------------------------------- -------- ------------------------------------
 ENAME                                                          VARCHAR2(20)
 AGE                                                            NUMBER

SQL> select * from ext_emp;
select * from ext_emp
*
ERROR at line 1:
ORA-29913: error in executing ODCIEXTTABLEOPEN callout
ORA-29400: data cartridge error
error opening file EXT_EMP_2604_4584.log

select * from abc1

ORA-29913: error in executing ODCIEXTTABLEFETCH callout
ORA-30653: reject limit reached