Today I rediscovered a feature of Oracle that is in since 10i. In 12c it was extended.
What is it all about? I am able to use dumps that where created with data pump as a file for external tables. But not enough I can also create an external table using CTAS (create table as select). Let’s see the simple steps to do so.
First I need a directory to write into. There are two options. First I grant the right as seen below to the user in need or I create the directory with the privileged user and grant the right to the directory to the user.
GRANT CREATE ANY DIRECTORY TO SCOTT;
As SCOTT I may now create the need directory. Oracle needs access to that directory.
CREATE OR REPLACE DIRECTORY ext_dir AS '/u01/userhome/oracle/ext_tables';
Directory EXT_DIR created.
Next I may create the external table with the data pump access driver. This is done with “TYPE ORACLE_DATAPUMP”.
CREATE TABLE ext_emp
ORGANIZATION EXTERNAL
(
TYPE ORACLE_DATAPUMP
DEFAULT DIRECTORY ext_dir
LOCATION ('ext_emp.dmp')
)
AS SELECT * FROM emp;
Table EXT_EMP created.
Now I can already access the external table
SELECT * FROM ext_emp;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
------ ---------- --------- ------ --------- ------ ------ ----------
7369 SMITH CLERK 7902 17-DEC-80 800 20
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
7566 JONES MANAGER 7839 02-APR-81 2975 20
7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
7698 BLAKE MANAGER 7839 01-MAY-81 2850 30
7782 CLARK MANAGER 7839 09-JUN-81 2450 10
7788 SCOTT ANALYST 7566 19-APR-87 3000 20
7839 KING PRESIDENT 17-NOV-81 5000 10
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
7876 ADAMS CLERK 7788 23-MAY-87 1100 20
7900 JAMES CLERK 7698 03-DEC-81 950 30
7902 FORD ANALYST 7566 03-DEC-81 3000 20
7934 MILLER CLERK 7782 23-JAN-82 1300 10
14 rows selected.
The definition is the same as the table was.
DESC ext_emp
Name Null? Type
-------- ----- ------------
EMPNO NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
COMM NUMBER(7,2)
DEPTNO NUMBER(2)
Some additional thoughts:
- No change of data possible. Once created it is read only
- Parallel is possible
- Compression is possible but only with “Advanced Compression”
It is a simple way to use external tables. No need to think about the format. No need to think about conversions. It is all done for you. Isn’t this great.
For more information just visit:
Oracle External Table Documentation
Oracle External Table Documentation – Oracle Data Pump Access Driver