Описание тега external-tables
To be used for External tables. These tables don't necessarily have data in the data warehouse(or database directory).
Hive
An EXTERNAL table points to any HDFS location for its storage, rather than being stored in a folder specified by the configuration property hive.metastore.warehouse.dir(Location of default database for the warehouse).
Oracle
External tables allow Oracle to query data that is stored outside the database in flat files. The ORACLE_LOADER driver can be used to access any data stored in any format that can be loaded by SQL*Loader. No DML can be performed on external tables but they can be used for query, join and sort operations.