This section lists restrictions to be aware of then you use the ORACLE_LOADER access driver.
Exporting and importing of external tables with encrypted columns is not supported.
Column processing: By default, the external tables feature fetches all columns defined for an external table. This guarantees a consistent result set for all queries. However, for performance reasons you can decide to process only the referenced columns of an external table, thus minimizing the amount of data conversion and data handling required to execute a query. In this case, a row that is rejected because a column in the row causes a data type conversion error will not get rejected in a different query if the query does not reference that column. You can change this column-processing behavior with the ALTER TABLE command.
An external table cannot load data into a LONG column.
SQL strings cannot be specified in access parameters for the ORACLE_LOADER access driver. As a workaround, you can use the DECODE clause in the SELECT clause of the statement that is reading the external table. Alternatively, you can create a view of the external table that uses the DECODE clause and select from that view rather than the external table.
The use of the backslash character (\) within strings is not supported in external tables. See "Use of the Backslash Escape Character".
When identifiers (for example, column or table names) are specified in the external table access parameters, certain values are considered to be reserved words by the access parameter parser. If a reserved word is used as an identifier, then it must be enclosed in double quotation marks.