Synopsis

ALTER EXTERNAL TABLE name action [, ... ]

  ADD [COLUMN] new_column type
  DROP [COLUMN] column [RESTRICT|CASCADE]
  ALTER [COLUMN] column TYPE type [USING expression]
  OWNER TO new_owner

Description

ALTER EXTERNAL TABLE changes the definition of an existing external table. These are the supported ALTER EXTERNAL TABLE actions:

• ADD COLUMN — Adds a new column to the external table definition.
• DROP COLUMN — Drops a column from the external table definition. If you drop readable external table columns, it only changes the table definition in Greenplum Database. The CASCADE keyword is required if anything outside the table depends on the column, such as a view that references the column.
• ALTER COLUMN TYPE — Changes the data type of a table column.
• OWNER — Changes the owner of the external table to the specified user.

You must own the external table to use ALTER EXTERNAL TABLE. To change the schema of an external table, you must also have CREATE privilege on the new schema. To alter the owner, you must also be a direct or indirect member of the new owning role, and that role must have CREATE privilege on the external table's schema. A superuser has these privileges automatically.

Changes to the external table definition with either ALTER EXTERNAL TABLE or ALTER TABLE do not affect the external data.

The ALTER EXTERNAL TABLE and ALTER TABLE commands cannot modify the type external table (read, write, web), the table FORMAT information, or the location of the external data. To modify this information, you must drop and recreate the external table definition.

Parameters

name

The name (possibly schema-qualified) of an existing external table definition to alter.

column

Name of an existing column.

new_column

Name of a new column.

USING expression

Optional if an implicit or assignment cast exists from the old column data type to new data type. The clause is required if there is no implicit or assignment cast.

The USING clause does not affect the external data.

type

Data type of the new column, or new data type for an existing column.

new_owner

The role name of the new owner of the external table.

CASCADE

Automatically drop objects that depend on the dropped column, such as a view that references the column.

RESTRICT

Refuse to drop the column or constraint if there are any dependent objects. This is the default behavior.

Examples

Add a new column to an external table definition:

ALTER EXTERNAL TABLE ext_expenses ADD COLUMN manager text;

Change the owner of an external table:

ALTER EXTERNAL TABLE ext_data OWNER TO jojo;

Change the data type of an external table:

ALTER EXTERNAL TABLE ext_leads ALTER COLUMN acct_code TYPE integer USING acct_code::integer

When altering the column data type from text to integer, the USING clause is required but does not affect the external data.

Compatibility

ALTER EXTERNAL TABLE is a Greenplum Database extension. There is no ALTER EXTERNAL TABLE statement in the SQL standard or regular PostgreSQL.

See Also

CREATE EXTERNAL TABLE, DROP EXTERNAL TABLE, ALTER TABLE