Oracle allows you read-only access to data in external tables. External tables are defined as tables that do not reside in the database, and can be in any format for which an access driver is provided. By providing with metadata describing an external table, Oracle is able to expose the data in the external table as if it were data residing in a regular database table. The external data can be queried directly and in parallel using SQL.

You can, for example, select, join, or sort external table data. You can also create views and synonyms for external tables. However, no DML operations (UPDATE, INSERT, or DELETE) are possible, and no indexes can be created, on external tables.

The DBMS_STATS package can be used for gathering statistics for external tables. The ANALYZE statement is not supported for gathering statistics for external tables.

You create external tables using the ORGANIZATION EXTERNAL clause of the CREATE TABLE statement. You are not in fact creating a table; that is, an external table does not have any extents associated with it. Rather, you are creating metadata in the data dictionary that enables you to access external data.

The following example creates an external table, then uploads the data to a database table.

EXAMPLE: Creating an External Table and Loading Data
The file empxt1.dat contains the following sample data:

360,Jane,Janus,ST_CLERK,121,17-MAY-2001,3000,0,50,jjanus
361,Mark,Jasper,SA_REP,145,17-MAY-2001,8000,.1,80,mjasper
362,Brenda,Starr,AD_ASST,200,17-MAY-2001,5500,0,10,bstarr
363,Alex,Alda,AC_MGR,145,17-MAY-2001,9000,.15,80,aalda


The file empxt2.dat contains the following sample data:

401,Jesse,Cromwell,HR_REP,203,17-MAY-2001,7000,0,40,jcromwel
402,Abby,Applegate,IT_PROG,103,17-MAY-2001,9000,.2,60,aapplega
403,Carol,Cousins,AD_VP,100,17-MAY-2001,27000,.3,90,ccousins
404,John,Richardson,AC_ACCOUNT,205,17-MAY-2001,5000,0,110,jrichard


The following SQL statements create an external table in the hr schema named admin_ext_employees and load its data into the hr.employees table.

CONNECT / AS SYSDBA;
-- Set up directories and grant access to hr
CREATE OR REPLACE DIRECTORY admin_dat_dir
AS '/net/dlsun301/private6/examples/submitted/ADMIN/flatfiles/data';
CREATE OR REPLACE DIRECTORY admin_log_dir
AS '/net/dlsun301/private6/examples/submitted/ADMIN/flatfiles/log';
CREATE OR REPLACE DIRECTORY admin_bad_dir
AS '/net/dlsun301/private6/examples/submitted/ADMIN/flatfiles/bad';
GRANT READ ON DIRECTORY admin_dat_dir TO hr;
GRANT WRITE ON DIRECTORY admin_log_dir TO hr;
GRANT WRITE ON DIRECTORY admin_bad_dir TO hr;
-- hr connects
CONNECT hr/hr
-- create the external table
CREATE TABLE admin_ext_employees
(employee_id NUMBER(4),
first_name VARCHAR2(20),
last_name VARCHAR2(25),
job_id VARCHAR2(10),
manager_id NUMBER(4),
hire_date DATE,
salary NUMBER(8,2),
commission_pct NUMBER(2,2),
department_id NUMBER(4),
email VARCHAR2(25)
)
ORGANIZATION EXTERNAL
(
TYPE ORACLE_LOADER
DEFAULT DIRECTORY admin_dat_dir
ACCESS PARAMETERS
(
records delimited by newline
badfile admin_bad_dir:'empxt%a_%p.bad'
logfile admin_log_dir:'empxt%a_%p.log'
fields terminated by ','
missing field values are null
( employee_id, first_name, last_name, job_id, manager_id,
hire_date char date_format date mask "dd-mon-yyyy",
salary, commission_pct, department_id, email
)
)
LOCATION ('empxt1.dat', 'empxt2.dat')
)
PARALLEL
REJECT LIMIT UNLIMITED;
-- enable parallel for loading (good if lots of data to load)
ALTER SESSION ENABLE PARALLEL DML;
-- load the data in hr employees table
INSERT INTO employees (employee_id, first_name, last_name, job_id, manager_id,
hire_date, salary, commission_pct, department_id, email)
SELECT * FROM admin_ext_employees;


Hope it helps u