Modifying External Tables

Altering External Tables

You can use any of the ALTER TABLE clauses shown in Table 1 below to change the characteristics of an external table. No other clauses are permitted.

Table 1: ALTER TABLE Clauses for External Tables

ALTER TABLE Clause	Description	Example
REJECT LIMIT	Changes the reject limit	ALTER TABLE admin_ext_employees REJECT LIMIT 100;
PROJECT COLUMN	Determines how the access driver validates rows in subsequent queries: PROJECT COLUMN REFERENCED: the access driver processes only the columns in the select list of the query. This setting may not provide a consistent set of rows when querying a different column list from the same external table. This is the default. PROJECT COLUMN ALL: the access driver processes all of the columns defined on the external table. This setting always provides a consistent set of rows when querying an external table.	ALTER TABLE admin_ext_employees PROJECT COLUMN REFERNCED; ALTER TABLE admin_ext_employees PROJECT COLUMN ALL;
DEFAULT DIRECTORY	Changes the default directory specification	ALTER TABLE admin_ext_employees DEFAULT DIRECTORY admin_dat2_dir;
ACCESS PARAMETERS	Allows access parameters to be changed without dropping and re-creating the external table metadata	ALTER TABLE admin_ext_employees ACCESS PARAMETERS (FIELDS TERMINATED BY ';');
LOCATION	Allows data sources to be changed without dropping and re-creating the external table metadata	ALTER TABLE admin_ext_employees LOCATION ('empxt3.txt', 'empxt4.txt');
PARALLEL	No difference from regular tables. Allows degree of parallelism to be changed.	No new syntax
ADD COLUMN	No difference from regular tables. Allows a column to be added to an external table. Virtual columns are not permitted.	No new syntax
MODIFY COLUMN	No difference from regular tables. Allows an external table column to be modified. Virtual columns are not permitted.	No new syntax
SET UNUSED	Transparently converted into an ALTER TABLE DROP COLUMN command. Because external tables consist of metadata only in the database, theDROP COLUMN command performs equivalently to the SET UNUSEDcommand.	No new syntax
DROP COLUMN	No difference from regular tables. Allows an external table column to be dropped.	No new syntax
RENAME TO	No difference from regular tables. Allows external table to be renamed.	No new syntax