外部表可以实现，通过数据库对象直接访问目录文件里的格式数据，加载方式分为两种oracle_loader和oracle_datapump,oracle_loader方式通过sqlldr引擎方式加载，访问flat格式文件；oracle_datapump通过datapump接口来加载，访问通过oracle_datapump方式卸载的dmp文件；
------oracle_loader
----自定义两个格式文件内容如下：
====a.dat====
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
====b.dat====
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
----创建需要的目录
CONNECT / AS SYSDBA;
-- Set up directories and grant access to hr
CREATE OR REPLACE DIRECTORY admin_dat_dir
AS '/u01/backup';
CREATE OR REPLACE DIRECTORY admin_log_dir
AS '/u01/backup';
CREATE OR REPLACE DIRECTORY admin_bad_dir
AS '/u01/backup';
GRANT READ ON DIRECTORY admin_dat_dir TO sun;
GRANT WRITE ON DIRECTORY admin_log_dir TO sun;
GRANT WRITE ON DIRECTORY admin_bad_dir TO sun;
----通过loader方式创建外部表，直接通过表来查询操作
conn sun/sun
-- 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 ('a.dat', 'b.dat')
)
PARALLEL
REJECT LIMIT UNLIMITED;
create table emp as select * from admin_ext_employees;
SQL>
SQL> SELECT * FROM emp;
EMPLOYEE_ID FIRST_NAME LAST_NAME JOB_ID M
----------- -------------------- ------------------------- ---------- -
401 Jesse Cromwell HR_REP
402 Abby Applegate IT_PROG
403 Carol Cousins AD_VP
404 John Richardson AC_ACCOUNT
360 Jane Janus ST_CLERK
361 Mark Jasper SA_REP
362 Brenda Starr AD_ASST
363 Alex Alda AC_MGR
SQL> SELECT * FROM user_external_tables ;
no rows selected
[ora11@prim backup]$ ls -l
total 20
-rw-r--r-- 1 ora11 oinstall 228 Sep 6 21:17 a.dat
-rw-r--r-- 1 ora11 oinstall 252 Sep 6 21:17 b.dat
-rw-r--r-- 1 ora11 oinstall 2826 Sep 6 21:19 empxt000_2756.log
-rw-r--r-- 1 ora11 oinstall 3110 Sep 6 21:19 empxt000_2763.log
-rw-r--r-- 1 ora11 oinstall 3110 Sep 6 21:19 empxt001_2765.log
------oracle_datapump
----更多是实现数据迁移的功能，通过datapump方式卸载并迁移到其他系统；
----创建datapump方式的外部表，并将数据卸载到目录文件中；
SQL> CREATE TABLE admin_ext_employees
2 (employee_id ,
3 first_name ,
4 last_name ,
5 job_id ,
6 manager_id ,
7 hire_date ,
8 salary ,
9 commission_pct ,
10 department_id ,
11 email
12 )
13 ORGANIZATION EXTERNAL
14 (
15 TYPE ORACLE_DATAPUMP
16 DEFAULT DIRECTORY admin_dat_dir
17 LOCATION ('emp2.dmp'))
18 AS SELECT * FROM emp;
Table created.
----查询文件内容，大体是产生XML格式的文件
-rw-r----- 1 ora11 oinstall 12288 Sep 6 21:33 emp2.dmp
[ora11@prim backup]$ strings emp2.dmp
"SUN"."U"
x86_64/Linux 2.4.xx
----通过loader方式创建外部表，直接通过表来查询操作
SQL> CREATE TABLE admin_ext_employees2
2 (employee_id NUMBER(4),
3 first_name VARCHAR2(20),
4 last_name VARCHAR2(25),
5 job_id VARCHAR2(10),
6 manager_id NUMBER(4),
7 hire_date DATE,
8 salary NUMBER(8,2),
9 commission_pct NUMBER(2,2),
10 department_id NUMBER(4),
11 email VARCHAR2(25)
12 )
13 ORGANIZATION EXTERNAL
14 (
15 TYPE ORACLE_DATAPUMP
16 DEFAULT DIRECTORY admin_dat_dir
17 LOCATION ('emp2.dmp')) ;
Table created.
SQL>
SQL> SELECT * FROM admin_ext_employees2 ;
EMPLOYEE_ID FIRST_NAME LAST_NAME JOB_ID
----------- -------------------- ------------------------- ----------
401 Jesse Cromwell HR_REP
402 Abby Applegate IT_PROG
403 Carol Cousins AD_VP
404 John Richardson AC_ACCOUNT
360 Jane Janus ST_CLERK
361 Mark Jasper SA_REP
362 Brenda Starr AD_ASST
363 Alex Alda AC_MGR