三步教会你掌握oracle外表(external table)

edoiktixth

　　外表(external
table)就像普通的表对像一样，可以select等，只是它是只读的，数据库中只保存了表结构的描述，表数据却没有存放在数据库内，而是存放在了文件
系统上。当用户想偶尔使用数据库外的结构化数据时，用起外表来就非常方便，甚至比sqlldr都要方便的多。在这篇文章里，我们为大家演示了

三步就掌握oracle外表过程。通过这次学习，也许大家就会发展原来学习oracle也是好容易哦。

  

第一步：创建目录并授权。目录是数据文件的存放目标，数据文件通常要求是文本文件。这个过程在9i以前是需要配置utl_file_dir参数的。

sys@TEST>!ls /home/oracle/temp
user.ctl  userlist.txt  user.log
rudolf@TEST>
sys@TEST>conn system/alibaba
Connected.
sys@TEST>
sys@TEST>CREATE DIRECTORY TEMP AS '/home/oracle/temp/';
Directory created.
sys@TEST>grant read,write on directory TEMP to rudolf;
Grant succeeded.
　　第二步：创建外表与测试

rudolf@TEST>CREATE TABLE "USERLIST"
2  (
3    ID NUMBER,
4    USERNAME VARCHAR2(30),
5    EMAIL VARCHAR2(128)
6  )
7  ORGANIZATION external
8  (
9    TYPE oracle_loader
10    DEFAULT DIRECTORY TEMP
11    ACCESS PARAMETERS
12    (
13      RECORDS DELIMITED BY NEWLINE CHARACTERSET US7ASCII
14      BADFILE 'TEMP':'userlist.bad'
15      DISCARDFILE 'TEMP':'userlist.dis'
16      LOGFILE 'TEMP':'user.log'
17      READSIZE 1048576
18      FIELDS TERMINATED BY "," OPTIONALLY ENCLOSED BY '"' LDRTRIM
19      MISSING FIELD VALUES ARE NULL
20      REJECT ROWS WITH ALL NULL FIELDS
21      (
22        ID CHAR(30)
23          TERMINATED BY "," OPTIONALLY ENCLOSED BY '"',
24        USERNAME CHAR(30)
25          TERMINATED BY "," OPTIONALLY ENCLOSED BY '"',
26        EMAIL CHAR(128)
27          TERMINATED BY "," OPTIONALLY ENCLOSED BY '"'
28      )
29    )
30    location
31    (
32      'userlist.txt'
33    )
34  )REJECT LIMIT UNLIMITED
35   
rudolf@TEST>/
Table created.
rudolf@TEST>l
1  select id,username from userlist where rownum < 10
2*
rudolf@TEST>/
ID USERNAME
---------- ------------------------------
1 RudolfLu
3 tomgu
6 coug
7 chao_ping
8 parrotao
9 cnoug
10 FilsDeDragon
11 Dragon
9 rows selected.
　　瞧，成功了。外表就这么简单。可是只有二步啊，第三步在哪里呢？你也许会问。还有啊，userlist.txt要固定的格式吗？create table...的语法这样的狂复杂，每一项都是什么含义呢？
　　
　　第三步：理解外表数据结构与create table ... organization
external语法。大家都用过sqlldr吧？外表的数据文件的结构呢就同sqlldr能读的数据文件结构一样了。那么语法呢？嘿嘿，别急，让我们先
来做个sqlldr的练习吧：

[oracle@rac1 temp]$ head -10 userlist.txt  
1,"RudolfLu"
3,"tomgu"
6,"coug"
7,"chao_ping"
8,"parrotao"
9,"cnoug"
10,"FilsDeDragon"
11,"Dragon"
15,"Xavier"
[oracle@rac1 temp]$ cat user.ctl  
LOAD
INFILE '/home/oracle/temp/userlist.txt'
badfile '/home/oracle/temp/userlist.bad'
discardfile '/home/oracle/temp/userlist.dis'
APPEND
INTO TABLE userlist
fields terminated by ',' optionally enclosed by '"'
trailing nullcols
( id  char(30),
username char(30)
)
rudolf@TEST>create table userlist
2  (id  number,
3   username varchar2(30)  
4  );
Table created.
rudolf@TEST>!
[oracle@rac1 temp]$ sqlldr rudolf/nix@test2.world control=./user.ctl external_table=GENERATE_ONLY
　　注意，我们加了一个external_table的参数。它的作用是告诉sqlldr不用真实load数据，而是生成包含external table 创建脚本的log文件。

[oracle@rac1 temp]$ ls
user.ctl  userlist.txt  user.log
[oracle@rac1 temp]$ cat user.log  
SQL*Loader: Release 9.2.0.4.0 - Production on Wed Dec 10 20:50:19 2003
Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.
Control File:   ./user.ctl
Data File:      /home/oracle/temp/userlist.txt
Bad File:     /home/oracle/temp/userlist.bad
Discard File: /home/oracle/temp/userlist.dis  
...
CREATE DIRECTORY statements needed for files
------------------------------------------------------------------------
CREATE DIRECTORY SYS_SQLLDR_XT_TMPDIR_00000 AS '/home/oracle/temp/'
CREATE TABLE statement for external table:
------------------------------------------------------------------------
CREATE TABLE "SYS_SQLLDR_X_EXT_USERLIST"  
(
ID NUMBER,
USERNAME VARCHAR2(30)
)
ORGANIZATION external  
(
TYPE oracle_loader
DEFAULT DIRECTORY SYS_SQLLDR_XT_TMPDIR_00000
ACCESS PARAMETERS  
(
RECORDS DELIMITED BY NEWLINE CHARACTERSET US7ASCII
BADFILE 'SYS_SQLLDR_XT_TMPDIR_00000':'userlist.bad'
DISCARDFILE 'SYS_SQLLDR_XT_TMPDIR_00000':'userlist.dis'
LOGFILE 'user.log_xt'
READSIZE 1048576
FIELDS TERMINATED BY "," OPTIONALLY ENCLOSED BY '"' LDRTRIM  
MISSING FIELD VALUES ARE NULL  
REJECT ROWS WITH ALL NULL FIELDS  
(
ID CHAR(30)
TERMINATED BY "," OPTIONALLY ENCLOSED BY '"',
USERNAME CHAR(30)
TERMINATED BY "," OPTIONALLY ENCLOSED BY '"'    )
)
location  
(
'userlist.txt'
)
)REJECT LIMIT UNLIMITED
...
　　瞧，原来我们更本不用担心怎么写create external table的语句呢。sqlldr就可以帮我们生成了！　

  

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