ALTER FOREIGN TABLE - Hologres - Alibaba Cloud Documentation Center

You can execute the ALTER FOREIGN TABLE statement to modify a foreign table. This topic describes how to execute the ALTER FOREIGN TABLE statement to rename a foreign table, add columns to a foreign table, or drop columns from a foreign table.

Limits

Hologres allows you to execute the ALTER FOREIGN TABLE statement only to rename a foreign table, add columns to a foreign table, or drop columns from a foreign table.

Rename a foreign table

Syntax:

ALTER FOREIGN TABLE [ IF EXISTS ] name RENAME TO new_name;

Sample SQL statement:

ALTER FOREIGN TABLE test RENAME TO new_test_table;

Add a column to a table

Hologres does not automatically update the schema of a created foreign table after columns are added to a mapped MaxCompute table. To query values of the added columns by using the foreign table, you must manually add the columns to the foreign table.

Note

You cannot add columns to a shared cluster by executing the following statements. For more information about how to add columns to a shared cluster, see IMPORT FOREIGN SCHEMA.

Syntax:

ALTER FOREIGN TABLE IF EXISTS table_name ADD COLUMN new_column_name data_type;

Sample SQL statements:

ALTER FOREIGN TABLE bank
 ADD COLUMN  cons_conf_idx float8,
 ADD COLUMN  euribor3m float8;

Drop a column

Syntax:

ALTER FOREIGN TABLE IF EXISTS table_name DROP COLUMN column_name;

Sample SQL statements:

ALTER FOREIGN TABLE bank
 DROP COLUMN  cons_conf_idx;