The access parameters clause contains comments, record formatting, and field formatting information.
The description of the data in the data source is separate from the definition of the external table. This means that:
The source file can contain more or fewer fields than there are columns in the external table
The data types for fields in the data source can be different from the columns in the external table
The access driver ensures that data from the data source is processed so that it matches the definition of the external table.
The syntax for the
access_parameters clause is as follows:
Oracle Database SQL Language Reference for information about specifying
opaque_format_spec when using the SQL
CREATE TABLE...ORGANIZATION EXTERNAL statement
--This is a comment. --This is another comment. RECORDS DELIMITED BY NEWLINE
All text to the right of the double hyphen is ignored, until the end of the line.
record_format_info clause is an optional clause that contains information about the record, such as its format, the character set of the data, and what rules are used to exclude records from being loaded. For a full description of the syntax, see "record_format_info Clause".
field_definitions clause is used to describe the fields in the data file. If a data file field has the same name as a column in the external table, then the data from the field is used for that column. For a full description of the syntax, see "field_definitions Clause".
column_transforms clause is an optional clause used to describe how to load columns in the external table that do not map directly to columns in the data file. This is done using the following transforms:
LOBFILE. For a full description of the syntax, see "column_transforms Clause".