A newer version of this documentation is available. Click here to view the most up-to-date release of the Greenplum 5.x documentation.


Changes the definition of an external table.


ALTER EXTERNAL TABLE name action [, ... ]

where action is one of:

  ADD [COLUMN] new_column type
  ALTER [COLUMN] column TYPE type [USING expression]
  OWNER TO new_owner


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.


The name (possibly schema-qualified) of an existing external table definition to alter.
Name of an existing 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.
Data type of the new column, or new data type for an existing column.
The role name of the new owner of the external table.
Automatically drop objects that depend on the dropped column, such as a view that references the column.
Refuse to drop the column or constraint if there are any dependent objects. This is the default behavior.


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:


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.


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