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 data types 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.
SQL> CREATE TABLE inv_part_1_xt 2 ORGANIZATION EXTERNAL 3 ( 4 TYPE ORACLE_DATAPUMP 5 DEFAULT DIRECTORY def_dir1 6 LOCATION ('inv_p1_xt.dmp') 7 ) 8 AS SELECT * FROM oe.inventories WHERE warehouse_id < 5; Table created. SQL> DROP TABLE inv_part_1_xt; SQL> CREATE TABLE inv_part_1_xt 2 ORGANIZATION EXTERNAL 3 ( 4 TYPE ORACLE_DATAPUMP 5 DEFAULT directory def_dir1 6 LOCATION ('inv_p2_xt.dmp') 7 ) 8 AS SELECT * FROM oe.inventories WHERE warehouse_id >= 5; Table created. SQL> CREATE TABLE inv_part_all_xt 2 ( 3 PRODUCT_ID NUMBER(6), 4 WAREHOUSE_ID NUMBER(3), 5 QUANTITY_ON_HAND NUMBER(8) 6 ) 7 ORGANIZATION EXTERNAL 8 ( 9 TYPE ORACLE_DATAPUMP 10 DEFAULT DIRECTORY def_dir1 11 LOCATION ('inv_p1_xt.dmp','inv_p2_xt.dmp') 12 ); Table created. SQL> SELECT * FROM inv_part_all_xt MINUS SELECT * FROM oe.inventories; no rows selected