Help Center/ GaussDB(DWS)/ SQL Syntax Reference/ SQL Syntax Reference (9.1.0.x)/ DDL Syntax/ ALTER FOREIGN TABLE (for HDFS or OBS)
Updated on 2024-09-02 GMT+08:00
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ALTER FOREIGN TABLE (for HDFS or OBS)

Function

Modifies an HDFS or OBS foreign table.

Precautions

None

Syntax

  • Set a foreign table's attributes: 
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    ALTER FOREIGN TABLE [ IF EXISTS ]  table_name
    OPTIONS ( {[ ADD | SET | DROP ] option ['value']} [, ... ]);
  • Set the owner of the foreign table: 
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    ALTER FOREIGN TABLE [ IF EXISTS ] tablename 
    OWNER TO new_owner;
  • Update a foreign table column: 
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    ALTER FOREIGN TABLE [ IF EXISTS ] table_name
    MODIFY ( { column_name data_type | column_name [ CONSTRAINT constraint_name ] NOT NULL [ ENABLE ] | column_name [ CONSTRAINT constraint_name ] NULL } [, ...] );
  • Modify the column of the foreign table: 
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    ALTER FOREIGN TABLE [ IF EXISTS ] tablename 
    action [, ... ];
    The action syntax is as follows: 
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    ALTER [ COLUMN ] column_name [ SET DATA ] TYPE data_type
   | ALTER [ COLUMN ] column_name { SET | DROP } NOT NULL
   | ALTER [ COLUMN ] column_name SET STATISTICS [PERCENT] integer
   | ALTER [ COLUMN ] column_name OPTIONS ( {[ ADD | SET | DROP ] option ['value'] } [, ... ])
   | MODIFY column_name data_type
   | MODIFY column_name [ CONSTRAINT constraint_name ] NOT NULL [ ENABLE ]
   | MODIFY column_name [ CONSTRAINT constraint_name ] NULL

    For details, see ALTER TABLE.

  • Add a foreign table informational constraint: 
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    ALTER FOREIGN TABLE [ IF EXISTS ] tablename
    ADD [ CONSTRAINT constraint_name ]
    { PRIMARY KEY | UNIQUE } ( column_name )
    [ NOT ENFORCED [ ENABLE QUERY OPTIMIZATION | DISABLE QUERY OPTIMIZATION ] | ENFORCED ];

    For parameters about adding an informational constraint to a foreign table, see Parameter Description.

  • Remove a foreign table informational constraint. 
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    ALTER FOREIGN TABLE [ IF EXISTS ] tablename 
    DROP CONSTRAINT constraint_name ;
  • Set the row-level access control switch (supported by cluster versions 9.1.0 and later). 
    ALTER FOREIGN TABLE [ IF EXISTS ] tablename
        ENABLE | DISABLE | FORCE | NO FORCE ROW LEVEL SECURITY

Parameter Description

  • IF EXISTS

    Sends a notification instead of an error if no tables have identical names. The notification prompts that the table you are querying does not exist.

  • tablename

    Specifies the name of an existing foreign table to be modified.

    Value range: an existing foreign table name

  • new_owner

    Specifies the new owner of the foreign table.

    Value range: A string indicating a valid user name.

  • data_type

    Specifies the new type for an existing column.

    Value range: A string compliant with the identifier naming rules.

  • constraint_name

    Specifies the name of a constraint to add or delete.

  • column_name

    Specifies the name of an existing column.

    Value range: a string. It must comply with the naming convention.

For details on how to modify other parameters in the foreign table, such as IF EXISTS, see Parameter Description in ALTER TABLE.

Examples

Change the type of the r_name column to text in the ft_region foreign table.

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ALTER FOREIGN TABLE ft_region ALTER r_name TYPE TEXT;
Run the following command to mark the r_name column of the ft_region foreign table as not null: 
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ALTER FOREIGN TABLE ft_region ALTER r_name SET NOT NULL;

Helpful Links

CREATE FOREIGN TABLE (SQL on OBS or Hadoop), DROP FOREIGN TABLE

Parent topic: DDL Syntax