參考文檔(11gr2的)：https://docs.oracle.com/cd/E11882_01/server.112/e22490/et_dp_driver.htm#SUTIL500
測試環境：RDBMS 19.0.0.0
文檔中關於DATAPUMP驅動的外部表的一些說明
Unloading and Loading Data with the ORACLE_DATAPUMP Access Driver
As part of creating an external table with a SQL CREATE TABLE AS SELECT statement, the ORACLE_DATAPUMP access driver can write data to a dump file. The data in the file is written in a binary format that can only be read by the ORACLE_DATAPUMP access driver. Once the dump file is created, it cannot be modified (that is, no data manipulation language (DML) operations can be performed on it). However, the file can be read any number of times and used as the dump file for another external table in the same database or in a different database.
谷歌翻譯下，大概如下：
作爲使用SQL CREATE table As SELECT語句創建外部表的一部分，ORACLE DATAPUMP訪問驅動程序可以將數據寫入轉儲文件。文件中的數據以二進制格式寫入，只能由ORACLE DATAPUMP訪問驅動程序讀取。一旦創建了轉儲文件，就不能對其進行修改(即不能對其執行任何數據操作語言(DML)操作)。但是，該文件可以被讀取任意次數，並用作同一數據庫或不同數據庫中的另一個外部表的轉儲文件。
--外部表的並行
Parallel Loading and Unloading
The dump file must be on a disk big enough to hold all the data being written. If there is insufficient space for all of the data, then an error is returned for the CREATE TABLE AS SELECT statement. One way to alleviate the problem is to create multiple files in multiple directory objects (assuming those directories are on different disks) when executing the CREATE TABLE AS SELECT statement. Multiple files can be created by specifying multiple locations in the form directory:file in the LOCATION clause and by specifying the PARALLEL clause. Each parallel I/O server process that is created to populate the external table writes to its own file. The number of files in the LOCATION clause should match the degree of parallelization because each I/O server process requires its own files. Any extra files that are specified will be ignored. If there are not enough files for the degree of parallelization specified, then the degree of parallelization is lowered to match the number of files in the LOCATION clause.
-- 外部表的轉儲文件，可以被其他的外部表使用
Dump files populated by different external tables can all be specified in the LOCATION clause of another external table. For example, data from different production databases can be unloaded into separate files, and then those files can all be included in an external table defined in a data warehouse. This provides an easy way of aggregating data from multiple sources. The only restriction is that the metadata for all of the external tables be exactly the same. This means that the character set, time zone, schema name, table name, and column names must all match. Also, the columns must be defined in the same order, and their datatypes must be exactly alike. This means that after you create the first external table you must drop it so that you can use the same table name for the second external table. This ensures that the metadata listed in the two dump files is the same and they can be used together to create the same external table.
-- 以下是測試
查看文件夾的路徑，並創建外部表
select owner,directory_name,directory_path from dba_directories where directory_name='DUMP';
create table emp_50
organization external
(
type oracle_datapump
default directory DUMP
location ('emp_50.dmp')
)
as select * from hr.employees where department_id=50
---文件夾是DUMP，路徑在/u01/dump下，創建一個外部表emp_50後，會在DUMP下生成dmp文件emp_50.dmp
SYS@test>select owner,directory_name,directory_path from dba_directories where directory_name='DUMP';
OWNE DIRECT DIRECTORY_PATH
---- ------ --------------------
SYS DUMP /u01/dump
SYS@test>
BB@test>create table emp_50
organization external
(
type oracle_datapump
default directory DUMP
location ('emp_50.dmp')
)
as select * from hr.employees where department_id=50 2 3 4 5 6 7 8
9 ;
表已創建。
BB@test>
[oracle@redhat762100 dump]$ ll *.dmp
-rw-r-----. 1 oracle oinstall 16384 Oct 21 13:01 emp_50.dmp
[oracle@redhat762100 dump]$
[oracle@redhat762100 dump]$ cp emp_50.dmp emp_50_1.dmp
[oracle@redhat762100 dump]$
-- 外部表創建的文件，只能被外部表訪問，是不可以被其他訪問的，比如，使用impdp訪問生成sql文件，會提示錯誤
[oracle@redhat762100 dump]$ impdp system/oracle directory=DUMP dumpfile=emp_50.dmp logfile=emp_50_1.log sqlfile=emp_50_1.sql
Import: Release 19.0.0.0.0 - Production on 星期一 10月 21 14:47:42 2019
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
連接到: Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
ORA-39001: 參數值無效
ORA-39000: 轉儲文件說明錯誤
ORA-39323: 無法從外部錶轉儲文件 "/u01/dump/emp_50.dmp" 加載數據
-- 可以使用linux的strings命令來查看dmp文件的內容：
[oracle@redhat762100 dump]$ strings emp_50_1.dmp
"BB"."U"
x86_64/Linux 2.4.xx
AL32UTF8
19.00.00.00.00
001:001:000001:000001
i<?xml version="1.0" encoding="UTF-8"?><ROWSET><ROW><STRMTABLE_T><VER_MAJOR>1</VER_MAJOR><VER_MINOR>0</VER_MINOR><VERS_DPAPI>3</VERS_DPAPI><ENDIANNESS>2</ENDIANNESS><CHARSET>AL32UTF8</CHARSET><NCHARSET>AL16UTF16</NCHARSET><DBTIMEZONE>+00:00</DBTIMEZONE><OWNER_NAME>BB</OWNER_NAME><NAME>EMP_50</NAME><COL_LIST><COL_LIST_ITEM><COL_NUM>1</COL_NUM><NAME>EMPLOYEE_ID</NAME><TYPE_NUM>2</TYPE_NUM><LENGTH>22</LENGTH><PRECISION_NUM>6</PRECISION_NUM><SCALE>0</SCALE><CHARSETID>0</CHARSETID><CHARSETFORM>0</CHARSETFORM><CHARLENGTH>0</CHARLENGTH></COL_LIST_ITEM><COL_LIST_ITEM><COL_NUM>2</COL_NUM><NAME>FIRST_NAME</NAME><TYPE_NUM>1</TYPE_NUM><LENGTH>20</LENGTH><CHARSETID>873</CHARSETID><CHARSETFORM>1</CHARSETFORM><CHARLENGTH>20</CHARLENGTH></COL_LIST_ITEM><COL_LIST_ITEM><COL_NUM>3</COL_NUM><NAME>LAST_NAME</NAME><TYPE_NUM>1</TYPE_NUM><LENGTH>25</LENGTH><CHARSETID>873</CHARSETID><CHARSETFORM>1</CHARSETFORM><CHARLENGTH>25</CHARLENGTH></COL_LIST_ITEM><COL_LIST_ITEM><COL_NUM>4</COL_NUM><NAME>EMAIL</NAME><TYPE_NUM>1</TYPE_NUM><LENGTH>25</LENGTH><CHARSETID>873</CHARSETID><CHARSETFORM>1</CHARSETFORM><CHARLENGTH>25</CHARLENGTH></COL_LIST_ITEM><COL_LIST_ITEM><COL_NUM>5</COL_NUM><NAME>PHONE_NUMBER</NAME><TYPE_NUM>1</TYPE_NUM><LENGTH>20</LENGTH><CHARSETID>873</CHARSETID><CHARSETFORM>1</CHARSETFORM><CHARLENGTH>20</CHARLENGTH></COL_LIST_ITEM><COL_LIST_ITEM><COL_NUM>6</COL_NUM><NAME>HIRE_DATE</NAME><TYPE_NUM>12</TYPE_NUM><LENGTH>7</LENGTH><CHARSETID>0</CHARSETID><CHARSETFORM>0</CHARSETFORM><CHARLENGTH>0</CHARLENGTH></COL_LIST_ITEM><COL_LIST_ITEM><COL_NUM>7</COL_NUM><NAME>JOB_ID</NAME><TYPE_NUM>1</TYPE_NUM><LENGTH>10</LENGTH><CHARSETID>873</CHARSETID><CHARSETFORM>1</CHARSETFORM><CHARLENGTH>10</CHARLENGTH></COL_LIST_ITEM><COL_LIST_ITEM><COL_NUM>8</COL_NUM><NAME>SALARY</NAME><TYPE_NUM>2</TYPE_NUM><LENGTH>22</LENGTH><PRECISION_NUM>8</PRECISION_NUM><SCALE>2</SCALE><CHARSETID>0</CHARSETID><CHARSETFORM>0</CHARSETFORM><CHARLENGTH>0</CHARLENGTH></COL_LIST_ITEM><COL_LIST_ITEM><COL_NUM>9</COL_NUM><NAME>COMMISSION_PCT</NAME><TYPE_NUM>2</TYPE_NUM><LENGTH>22</LENGTH><PRECISION_NUM>2</PRECISION_NUM><SCALE>2</SCALE><CHARSETID>0</CHARSETID><CHARSETFORM>0</CHARSETFORM><CHARLENGTH>0</CHARLENGTH></COL_LIST_ITEM><COL_LIST_ITEM><COL_NUM>10</COL_NUM><NAME>MANAGER_ID</NAME><TYPE_NUM>2</TYPE_NUM><LENGTH>22</LENGTH><PRECISION_NUM>6</PRECISION_NUM><SCALE>0</SCALE><CHARSETID>0</CHARSETID><CHARSETFORM>0</CHARSETFORM><CHARLENGTH>0</CHARLENGTH></COL_LIST_ITEM><COL_LIST_ITEM><COL_NUM>11</COL_NUM><NAME>DEPARTMENT_ID</NAME><TYPE_NUM>2</TYPE_NUM><LENGTH>22</LENGTH><PRECISION_NUM>4</PRECISION_NUM><SCALE>0</SCALE><CHARSETID>0</CHARSETID><CHARSETFORM>0</CHARSETFORM><CHARLENGTH>0</CHARLENGTH></COL_LIST_ITEM></COL_LIST></STRMTABLE_T></ROW></ROWSET>
Matthew
Weiss
MWEISS
650.123.1234
ST_MAN
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650.123.2234
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650.123.3234
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SVOLLMAN
650.123.4234
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KMOURGOS
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650.124.1214
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IMIKKILI
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[oracle@redhat762100 dump]$
-- 創建一個外部表，並行度3，這樣會在DUMP文件夾下生成3個dmp文件。
create table dba_objects_ex
organization external
(
type oracle_datapump
default directory DUMP
location ('dba_object01.dmp','dba_object02.dmp','dba_object03.dmp')
)
parallel 3
as select * from sys.dba_objects
SYS@test>create table dba_objects_ex
organization external
(
type oracle_datapump
default directory DUMP
location ('dba_object01.dmp','dba_object02.dmp','dba_object03.dmp')
)
parallel 3
as select * from sys.dba_objects 2 3 4 5 6 7 8 9
10 ;
表已創建。
SYS@test>
[oracle@redhat762100 dump]$ ll *.dmp
-rw-r-----. 1 oracle oinstall 3432448 Oct 21 14:57 dba_object01.dmp
-rw-r-----. 1 oracle oinstall 3358720 Oct 21 14:57 dba_object02.dmp
-rw-r-----. 1 oracle oinstall 3309568 Oct 21 14:57 dba_object03.dmp
-rw-r-----. 1 oracle oinstall 16384 Oct 21 13:02 emp_50_1.dmp
-rw-r-----. 1 oracle oinstall 16384 Oct 21 13:01 emp_50.dmp
[oracle@redhat762100 dump]$
-- 創建一個外部表，使用之前的dmp文件，使用上面的外部表生成的dba_object01-03.dmp文件
create table DBA_OBJECTS_EX1
(
owner VARCHAR2(128),
object_name VARCHAR2(128),
subobject_name VARCHAR2(128),
object_id NUMBER,
data_object_id NUMBER,
object_type VARCHAR2(23),
created DATE,
last_ddl_time DATE,
timestamp VARCHAR2(19),
status VARCHAR2(7),
temporary VARCHAR2(1),
generated VARCHAR2(1),
secondary VARCHAR2(1),
namespace NUMBER,
edition_name VARCHAR2(128),
sharing VARCHAR2(18),
editionable VARCHAR2(1),
oracle_maintained VARCHAR2(1),
application VARCHAR2(1),
default_collation VARCHAR2(100),
duplicated VARCHAR2(1),
sharded VARCHAR2(1),
created_appid NUMBER,
created_vsnid NUMBER,
modified_appid NUMBER,
modified_vsnid NUMBER
)
organization external
(
type oracle_datapump
default directory DUMP
location ('dba_object01.dmp','dba_object02.dmp','dba_object03.dmp')
)
;
SYS@test>create table DBA_OBJECTS_EX1
2 (
3 owner VARCHAR2(128),
object_name VARCHAR2(128),
subobject_name VARCHAR2(128),
4 5 6 object_id NUMBER,
data_object_id NUMBER,
object_type VARCHAR2(23),
created DATE,
last_ddl_time DATE,
7 timestamp VARCHAR2(19),
status VARCHAR2(7),
temporary VARCHAR2(1),
generated VARCHAR2(1),
secondary VARCHAR2(1),
8 namespace NUMBER,
edition_name VARCHAR2(128),
sharing VARCHAR2(18),
9 10 11 12 13 14 15 16 17 18 19 editionable VARCHAR2(1),
oracle_maintained VARCHAR2(1),
application VARCHAR2(1),
default_collation VARCHAR2(100),
duplicated VARCHAR2(1),
sharded VARCHAR2(1),
created_appid NUMBER,
created_vsnid NUMBER,
modified_appid NUMBER,
modified_vsnid NUMBER
)
organization external
(
type oracle_datapump
default directory DUMP
location ('dba_object01.dmp','dba_object02.dmp','dba_object03.dmp')
)
; 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
表已創建。
SYS@test>
-- 當然，也可以使用上面的外部表產生的dmp文件中的任何一個，這裏測試使用上面的外部表產生的其中兩個dmp文件
create table DBA_OBJECTS_EX2
(
owner VARCHAR2(128),
object_name VARCHAR2(128),
subobject_name VARCHAR2(128),
object_id NUMBER,
data_object_id NUMBER,
object_type VARCHAR2(23),
created DATE,
last_ddl_time DATE,
timestamp VARCHAR2(19),
status VARCHAR2(7),
temporary VARCHAR2(1),
generated VARCHAR2(1),
secondary VARCHAR2(1),
namespace NUMBER,
edition_name VARCHAR2(128),
sharing VARCHAR2(18),
editionable VARCHAR2(1),
oracle_maintained VARCHAR2(1),
application VARCHAR2(1),
default_collation VARCHAR2(100),
duplicated VARCHAR2(1),
sharded VARCHAR2(1),
created_appid NUMBER,
created_vsnid NUMBER,
modified_appid NUMBER,
modified_vsnid NUMBER
)
organization external
(
type oracle_datapump
default directory DUMP
location ('dba_object01.dmp','dba_object03.dmp')
)
;
SYS@test>create table DBA_OBJECTS_EX2
(
owner VARCHAR2(128),
object_name VARCHAR2(128),
subobject_name VARCHAR2(128),
object_id NUMBER,
data_object_id NUMBER,
object_type VARCHAR2(23),
created DATE,
last_ddl_time DATE,
timestamp VARCHAR2(19),
status VARCHAR2(7),
temporary VARCHAR2(1),
2 3 4 5 6 7 8 9 10 11 12 13 14 generated VARCHAR2(1),
secondary VARCHAR2(1),
namespace NUMBER,
edition_name VARCHAR2(128),
sharing VARCHAR2(18),
editionable VARCHAR2(1),
oracle_maintained VARCHAR2(1),
application VARCHAR2(1),
default_collation VARCHAR2(100),
duplicated VARCHAR2(1),
sharded VARCHAR2(1),
created_appid NUMBER,
created_vsnid NUMBER,
modified_appid NUMBER,
modified_vsnid NUMBER
)
organization external
(
type oracle_datapump
default directory DUMP
location ('dba_object01.dmp','dba_object03.dmp')
)
;
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
表已創建。
SYS@test>SYS@test>
-- 查詢數據，可以看到，是可以使用其中任何一個dmp文件創建外部表的。
SYS@test>select count(*) from DBA_OBJECTS_EX1 union all select count(*) from DBA_OBJECTS_EX2;
COUNT(*)
----------
72887
48887
SYS@test>
-- drop掉外部表，並不會刪除該外部表的dmp文件（自行測試，這裏不寫了）
-- 補充，比較適合的一個場景，每天需要將數據導入到測試環境進行查看，可以在測試環境創建一個外部表。每天從生產環境導出dmp文件，拷貝出來，覆蓋測試環境的文件即可。
END