oracle创建外部表

oracle db允许以只读的形式查询外部表。外部表可以存储在任何oracle db可以读取的存储设备中，其内容不在db中保存，db只保存external table的metadata，db可以查询（join、sort）external table，可以创建view、synonym，但不可以执行DML语句。

创建外部表语法create table ……orginzition external，可以把外部表假想为一个view，可以正常的做select。
analyze 和 虚拟列 表分析不使用与外部表

创建外部表语法
外部表文件：
example1.txt
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
example2.txt
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
创建外部表oracle可识别路径：

SQL> conn / as sysdba
SQL> create directory external_dir as ‘/u01/app/oracle/oradata/external‘;

Directory created.

SQL> grant read，write on directory external_dir to kevin;

Grant succeeded.

外部表的使用用户kevin，创建外部表

SQL> CREATE TABLE   ex_employees
  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_LOADER
16         DEFAULT DIRECTORY external_dir
17         ACCESS PARAMETERS
18         (
19           records delimited by newline
20           badfile external_dir:‘empxt%a_%p.bad‘
21           logfile  external_dir:‘empxt%a_%p.log‘
22           fields terminated by ‘,‘
23           missing field values are null
24           ( employee_id, first_name, last_name, job_id, manager_id,
25             hire_date char date_format date mask "dd-mon-yyyy",
26             salary, commission_pct, department_id, email
27           )
28         )
29         LOCATION (‘example1.txt‘, ‘example2.txt‘)
30       )
31       PARALLEL
32       REJECT LIMIT UNLIMITED;

Table created.

创建完成后可以可以通过cats把数据导入至数据库的表中，如果数据比较多，可以开启session level parallel导入

alter session enable parallel；
create table employee as select * from ex_employee;

EMPLOYEE_ID FIRST_NAME           LAST_NAME                 JOB_ID     MANAGER_ID HIRE_DATE     SALARY COMMISSION_PCT DEPARTMENT_ID EMAIL
----------- -------------------- ------------------------- ---------- ---------- --------- ---------- -------------- ------------- -------------------------
        360 Jane                 Janus                     ST_CLERK          121 17-MAY-01       3000              0            50 jjanus
        361 Mark                 Jasper                    SA_REP            145 17-MAY-01       8000             .1            80 mjasper
        362 Brenda               Starr                     AD_ASST           200 17-MAY-01       5500              0            10 bstarr
        363 Alex                 Alda                      AC_MGR            145 17-MAY-01       9000            .15            80 aalda

        401 Jesse                Cromwell                  HR_REP            203 17-MAY-01       7000              0            40 jcromwel
        402 Abby                 Applegate                 IT_PROG           103 17-MAY-01       9000             .2            60 aapplega
        403 Carol                Cousins                   AD_VP             100 17-MAY-01      27000             .3            90 ccousins
        404 John                 Richardson                AC_ACCOUNT        205 17-MAY-01       5000              0           110 jrichard


10 rows selected.

创建完成，外部表可以正常使用