inline-external-tables-18c

Inline External Tables in Oracle Database 18c

Oracle Database 18c allows you to access data in flat files using an
inline external table defined in a SELECT statement.

Inline External Tables

This is a step further than the ability to [46]override external table
parameters from a query introduced in Oracle Database 12c Release 2
(12.2).
* [47]Setup
* [48]Inline External Table
* [49]Security Implications
* [50]Miscellaneous

Related articles.
* [51]External Tables : All Articles
* [52]Override External Table Parameters From a Query in Oracle
Database 12c Release 2 (12.2)

Setup

In order to demonstrate an inline external table we need some data in
flat files. The following code spools out four CSV files with 1000 rows
each.
CONN / AS SYSDBA
ALTER SESSION SET CONTAINER = pdb1;

SET MARKUP CSV ON QUOTE ON
SET TRIMSPOOL ON LINESIZE 1000 FEEDBACK OFF PAGESIZE 0

SPOOL /tmp/gbr1.txt
SELECT 'GBR',
object_id,
owner,
object_name
FROM dba_objects
WHERE object_id <= 2000
AND rownum <= 1000;
SPOOL OFF

SPOOL /tmp/gbr2.txt
SELECT 'GBR',
object_id,
owner,
object_name
FROM dba_objects
WHERE object_id BETWEEN 2000 AND 3999
AND rownum <= 1000;
SPOOL OFF

SPOOL /tmp/ire1.txt
SELECT 'IRE',
object_id,
owner,
object_name
FROM dba_objects
WHERE object_id <= 2000
AND rownum <= 1000;
SPOOL OFF

SPOOL /tmp/ire2.txt
SELECT 'IRE',
object_id,
owner,
object_name
FROM dba_objects
WHERE object_id BETWEEN 2000 AND 3999
AND rownum <= 1000;
SPOOL OFF

SET MARKUP CSV OFF
SET TRIMSPOOL ON LINESIZE 1000 FEEDBACK OFF PAGESIZE 14

Create two directory objects to access these files. In this case both
are pointing to the same directory, but it will still allow us to see
the syntax.
CONN / AS SYSDBA
ALTER SESSION SET CONTAINER = pdb1;

CREATE OR REPLACE DIRECTORY tmp_dir1 AS '/tmp/';
GRANT READ, WRITE ON DIRECTORY tmp_dir1 TO test;

CREATE OR REPLACE DIRECTORY tmp_dir2 AS '/tmp/';
GRANT READ, WRITE ON DIRECTORY tmp_dir2 TO test;

CONN test/test@pdb1

Inline External Table

An inline external table allows the external table definition to be
placed in the FROM clause of a SQL statement using the EXTERNAL clause,
so there is no need for an external table to be explicitly created.
SELECT country_code, COUNT(*) AS amount
FROM EXTERNAL (
(
country_code VARCHAR2(3),
object_id NUMBER,
owner VARCHAR2(128),
object_name VARCHAR2(128)
)
TYPE oracle_loader
DEFAULT DIRECTORY tmp_dir1
ACCESS PARAMETERS (
RECORDS DELIMITED BY NEWLINE
BADFILE tmp_dir1
LOGFILE tmp_dir1:'inline_ext_tab_%a_%p.log'
DISCARDFILE tmp_dir1
FIELDS CSV WITH EMBEDDED TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
MISSING FIELD VALUES ARE NULL (
country_code,
object_id,
owner,
object_name
)
)
LOCATION ('gbr1.txt', 'gbr2.txt', 'ire1.txt', 'ire2.txt')
REJECT LIMIT UNLIMITED
) inline_ext_tab
GROUP BY country_code
ORDER BY 1;

COUNTRY_CODE AMOUNT
------------ ----------
GBR 2000
IRE 2000

SQL>

In the following example we use a different directory object, and
specify a different list of files in the LOCATION clause. This, not
surprisingly gives us a different result.
SELECT country_code, COUNT(*) AS amount
FROM EXTERNAL (
(
country_code VARCHAR2(3),
object_id NUMBER,
owner VARCHAR2(128),
object_name VARCHAR2(128)
)
TYPE oracle_loader
DEFAULT DIRECTORY tmp_dir2
ACCESS PARAMETERS (
RECORDS DELIMITED BY NEWLINE
BADFILE tmp_dir2
LOGFILE tmp_dir2:'inline_ext_tab_%a_%p.log'
DISCARDFILE tmp_dir2
FIELDS CSV WITH EMBEDDED TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
MISSING FIELD VALUES ARE NULL (
country_code,
object_id,
owner,
object_name
)
)
LOCATION ('gbr1.txt', 'gbr2.txt')
REJECT LIMIT UNLIMITED
) inline_ext_tab
GROUP BY country_code
ORDER BY 1;

COUNTRY_CODE AMOUNT
------------ ----------
GBR 2000

SQL>

The inline external table definition is a little ugly, so you may
prefer to put it into a WITH clause if you are planning to join it to
other tables.
WITH inline_ext_tab AS (
SELECT *
FROM EXTERNAL (
(
country_code VARCHAR2(3),
object_id NUMBER,
owner VARCHAR2(128),
object_name VARCHAR2(128)
)
TYPE oracle_loader
DEFAULT DIRECTORY tmp_dir2
ACCESS PARAMETERS (
RECORDS DELIMITED BY NEWLINE
BADFILE tmp_dir2
LOGFILE tmp_dir2:'inline_ext_tab_%a_%p.log'
DISCARDFILE tmp_dir2
FIELDS CSV WITH EMBEDDED TERMINATED BY ',' OPTIONALLY ENCLOSED BY '
"'
MISSING FIELD VALUES ARE NULL (
country_code,
object_id,
owner,
object_name
)
)
LOCATION ('gbr1.txt', 'gbr2.txt')
REJECT LIMIT UNLIMITED
)
)
SELECT country_code, COUNT(*) AS amount
FROM inline_ext_tab
GROUP BY country_code
ORDER BY 1;

COUNTRY_CODE AMOUNT
------------ ----------
GBR 2000

SQL>

Security Implications

Access to directory objects should be controlled carefully, regardless
of if you use external tables or not.

The security implications of dynamic access to directory objects and
external files is discussed [53]here.

Miscellaneous

Some thoughts and comments related to this functionality.
* As stated in the documentation, this functionality doesn't support
partitioned external tables, but that is irrelevant as you have
full control of the files being accessed, so there is no need to
consider partitioning.
* As mentioned above, there are security considerations related to
this functionality.
* It results in really ugly SQL.
* It could be useful in a situation where you don't have privilege to
create a metadata object, for example a read-only database.

For more information see:
* [54]Using Inline External Tables
* [55]External Tables : All Articles
* [56]Override External Table Parameters From a Query in Oracle
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Source .... : https://oracle-base.com/articles/18c/inline-external-tables-18c
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