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Querying external tables

Without loading data into your database, you can query external tables directly from flat files.

External tables are read-only tables in which the data is stored outside the database in flat files. The data can be queried like a virtual table. Metadata of an external table is created with the CREATE TABLE command. Without loading data into your database, you can query the data directly from flat files. (In Oracle 8i, you need to load that data using SQL*Loader.) Restriction: No DML operations are possible and no indexes can be created.

CREATE table emp_ext
( empno number,
  first_name char(30),
  last_naem  char(30)
ORGANIZATION EXTERNAL (
TYPE oracle_loader
DEFAULT DIRECTORY flatfile_dir
ACCESS PARAMETERS
( RECORDS DELIMITED BY NEWLINE
  FIELDS TERMINATED BY '~'
  BADFILE 'emp_ext.bad'
  LOGFILE 'emp_ext.log'
  MISSING FIELDS ARE NULL)
  LOCATION ('emp1.txt', 'emp2.txt'))
PARALLEL 5
REJECT LIMIT UNLIMITED;
In the above example, when the external table "emp_ext" is queried, the data is retrieved from the external data files.

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