Changes the definition of an external table.

Synopsis

ALTER EXTERNAL TABLE <name> <action> [, ... ]

where action is one of:

  ADD [COLUMN] <new_column> <type>
  DROP [COLUMN] <column> [RESTRICT|CASCADE]
  ALTER [COLUMN] <column> TYPE <type>
  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.

Use the ALTER TABLE command to perform these actions on an external table.

• Set (change) the table schema.
• Rename the table.
• Rename a table column.

You must own the external table to use ALTER EXTERNAL TABLE or ALTER 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.

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

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

Parent topic: SQL Commands