tajo-docs/src/main/sphinx/sql_language/alter_table.rst

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ALTER TABLE
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RENAME TABLE
========================

*Synopsis*

.. code-block:: sql

  ALTER TABLE <table_name> RENAME TO <new_table_name>

  For example:
  ALTER TABLE table1 RENAME TO table2;

This statement lets you change the name of a table to a different name.

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RENAME COLUMN
========================

*Synopsis*

.. code-block:: sql

  ALTER TABLE <table_name> RENAME COLUMN <column_name> TO <new_column_name>

  For example:
  ALTER TABLE table1 RENAME COLUMN id TO id2;

This statement will allow users to change a column's name.

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ADD COLUMN
========================

*Synopsis*

.. code-block:: sql

  ALTER TABLE <table_name> ADD COLUMN <column_name> <data_type>

  For example:
  ALTER TABLE table1 ADD COLUMN id text;

This statement lets you add new columns to the end of the existing column.

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SET PROPERTY
========================

*Synopsis*

.. code-block:: sql

  ALTER TABLE <table_name> SET PROPERTY (<key> = <value>, ...)

  For example:
  ALTER TABLE table1 SET PROPERTY 'timezone' = 'GMT-7'
  ALTER TABLE table1 SET PROPERTY 'text.delimiter' = '&'
  ALTER TABLE table1 SET PROPERTY 'compression.type'='RECORD','compression.codec'='org.apache.hadoop.io.compress.SnappyCodec'


This statement will allow users to change a table property.

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 DROP PARTITION
========================

*Synopsis*

.. code-block:: sql

  ALTER TABLE <table_name> [IF EXISTS] DROP PARTITION (<partition column> = <partition value>, ...) [PURGE]

  For example:
  ALTER TABLE table1 DROP PARTITION (col1 = 1 , col2 = 2)
  ALTER TABLE table1 DROP PARTITION (col1 = '2015' , col2 = '01', col3 = '11' )
  ALTER TABLE table1 DROP PARTITION (col1 = 'TAJO' ) PURGE

You can use ``ALTER TABLE DROP PARTITION`` to drop a partition for a table. This doesn't remove the data for a table. But if ``PURGE`` is specified, the partition data will be removed. The metadata is completely lost in all cases. An error is thrown if the partition for the table doesn't exist. You can use ``IF EXISTS`` to skip the error.

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REPAIR PARTITION
========================

Tajo stores a list of partitions for each table in its catalog. If partitions are manually added to the distributed file system, the metastore is not aware of these partitions. Running the ``ALTER TABLE REPAIR PARTITION`` statement ensures that the tables are properly populated.

*Synopsis*

.. code-block:: sql

  ALTER TABLE <table_name> REPAIR PARTITION

.. note::

  Even though an information of a partition is stored in the catalog, Tajo does not recover it when its partition directory doesn't exist in the file system.