Oracle外部表

1.外部表简介
外部表是Oracle9i之后来使用的。外部表是一类表的定义存在于数据库而数据不存在于数据库的表。
在数据库操作过程中可以对外部表进行select,join,sort操作也可以对外部表创建视图和同义词。但是不能在外部表上进行DML操作和创建索引。

外部表提供两种访问驱动。一种ORACLE_LOADER另一种ORACLE_DATAPUMP。默认驱动是ORACLE_LOADER。
ORACLE_LOADER驱动从外部文件中读数据。ORACLE_LOADER创建外部表的语法和SQL*Loader utility有异曲同工之妙。
ORACLE_DATAPUMP先通过外部表unload出数据然后通过外部表reload表。具体下面小节分析。

另外外部表的统计信息收集支持DBMS_STATS包但不支持ANALYZE。
而且外部表不支持虚拟列。

2.创建外部表
[oracle@localhost mydir]$ cat samp1.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
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

SQL> create or replace directory mydir as '/home/oracle/mydir';

Directory created.

SQL> grant read,write on directory mydir to scott;

Grant succeeded.

SQL> conn scott/tiger
Connected.

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 mydir
ACCESS PARAMETERS
(
records delimited by newline
badfile mydir:'badxt%a_%p.bad'
logfile mydir:'logxt%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 ('samp1.txt')
)
PARALLEL REJECT LIMIT UNLIMITED;

PARALLEL --指定查询时的并行度
REJECT LIMIT UNLIMITED --指定外部表查询错误数量

执行成功看产生的日志。

[oracle@localhost mydir]$ ls -al
total 20
drwxr-xr-x 2 oracle oinstall 4096 Nov 20 16:12 .
drwx------ 5 oracle oinstall 4096 Nov 20 15:53 ..
-rw-r--r-- 1 oracle oinstall 1413 Nov 20 16:12 logxt000_13688.log
-rw-r--r-- 1 oracle oinstall 1555 Nov 20 16:12 logxt000_16408.log
-rw-r--r-- 1 oracle oinstall 480 Nov 20 15:53 samp1.txt

[oracle@localhost mydir]$ cat logxt000_13688.log

LOG file opened at 11/20/15 16:12:03

Field Definitions for table ADMIN_EXT_EMPLOYEES
Record format DELIMITED BY NEWLINE
Data in file has same endianness as the platform
Rows with all null fields are accepted

Fields in Data Source:

EMPLOYEE_ID CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
FIRST_NAME CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
LAST_NAME CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
JOB_ID CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
MANAGER_ID CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
HIRE_DATE CHAR (80)
Date datatype DATE, date mask dd-mon-yyyy
Terminated by ","
Trim whitespace same as SQL Loader
SALARY CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
COMMISSION_PCT CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
DEPARTMENT_ID CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
EMAIL CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
[oracle@localhost mydir]$ cat logxt000_16408.log

LOG file opened at 11/20/15 16:12:03

Field Definitions for table ADMIN_EXT_EMPLOYEES
Record format DELIMITED BY NEWLINE
Data in file has same endianness as the platform
Rows with all null fields are accepted

Fields in Data Source:

EMPLOYEE_ID CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
FIRST_NAME CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
LAST_NAME CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
JOB_ID CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
MANAGER_ID CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
HIRE_DATE CHAR (80)
Date datatype DATE, date mask dd-mon-yyyy
Terminated by ","
Trim whitespace same as SQL Loader
SALARY CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
COMMISSION_PCT CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
DEPARTMENT_ID CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader
EMAIL CHAR (255)
Terminated by ","
Trim whitespace same as SQL Loader

Date Cache Statistics for table ADMIN_EXT_EMPLOYEES
Max Size: 1000
Entries : 1
Hits : 7
Misses : 0

logxt000_16408.log日志比logxt000_13688.log尾部多了一些统计信息。

查看外部表
SQL> select EMPLOYEE_ID,FIRST_NAME from ADMIN_EXT_EMPLOYEES;

EMPLOYEE_ID FIRST_NAME
----------- --------------------
360 Jane
361 Mark
362 Brenda
363 Alex
401 Jesse
402 Abby
403 Carol
404 John

3.外部表修改
能够使用于alter table下面子句来修改外部表访问参数
reject limit:ALTER TABLE admin_ext_employees REJECT LIMIT n;

project column: ALTER TABLE admin_ext_employees PROJECT COLUMN REFERENCED;
ALTER TABLE admin_ext_employees PROJECT COLUMN ALL;
default dectory:ALTER TABLE admin_ext_employees DEFAULT DIRECTORY admin_dat2_dir;

查看修改的属性
SQL> select OWNER,TABLE_NAME,REJECT_LIMIT,DEFAULT_DIRECTORY_NAME,PROPERTY from dba_external_tables;

OWNER TABLE_NAME REJECT_LIM DEFAULT_DIRECTORY_NAME PROPERTY
---------- ------------------------------ ---------- ------------------------------ ----------
SCOTT ADMIN_EXT_EMPLOYEES UNLIMITED MYDIR ALL

4.预处理外部表

SQL> create or replace directory mydir as '/home/oracle/mydir';

Directory created.

SQL> grant read,write,execute on directory mydir to scott;

Grant succeeded.

在/home/oracle/mydir下面创建一个文件
[oracle@localhost mydir]$ cat uncompress
/bin/gzip -cd $1
[oracle@localhost mydir]$ chmod +x uncompress

SQL> conn scott/tiger
Connected.
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 mydir
ACCESS PARAMETERS
(
records delimited by newline
PREPROCESSOR exec_file_dir:'uncompress'
badfile mydir:'badxt%a_%p.bad'
logfile mydir:'logxt%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 ('samp1.txt.gz')
)
PARALLEL
REJECT LIMIT UNLIMITED;

5.外部表的删除使用DROP TABLE语句这条语句仅仅删除数据库中的介质,对实际数据没有影响。
SQL> drop table admin_ext_employees;

Table dropped.

6.有关外部表的系统权限和对象。
外部表的系统权限
CREATE ANY TABLE
ALTER ANY TABLE
DROP ANY TABLE
SELECT ANY TABLE

外部表的对象权限
ALTER
SELECT