UPDATE

.. highlight:: cql

.. _update-statement:

UPDATE ^^^^^^

Updating a row is done using an UPDATE statement:

.. code-block::

update_statement: UPDATE table_name : [ USING update_parameter ( AND update_parameter )* ] : SET assignment ( ',' assignment )* : WHERE where_clause : [ IF ( EXISTS | condition ( AND condition )*) ] update_parameter: ( TIMESTAMP int_value | TTL int_value | TIMEOUT duration ) int_value: ( integer | bind_marker ) assignment: simple_selection '=' term : | column_name '=' column_name ( '+' | '-' ) term : | column_name '=' list_literal '+' column_name simple_selection: column_name : | column_name '[' term ']' : | column_name '.' field_name condition: simple_selection operator term

For instance:

.. code-block:: cql

UPDATE NerdMovies USING TTL 400
   SET director   = 'Joss Whedon',
       main_actor = 'Nathan Fillion',
       year       = 2005
 WHERE movie = 'Serenity';

UPDATE UserActions
   SET total = total + 2
   WHERE user = B70DE1D0-9908-4AE3-BE34-5573E5B09F14
     AND action = 'click';

The UPDATE statement writes one or more columns for a given row in a table. The :token:where_clause is used to select the row to update and must include all columns composing the PRIMARY KEY. Non-primary key columns are then set using the SET keyword.

Note that unlike in SQL, UPDATE does not check the prior existence of the row by default,

(except through IF_, see below):

the row is created if none existed before, and updated otherwise. Furthermore, there is no way to know whether creation or update occurred.

In an UPDATE statement, all updates within the same partition key are applied atomically, meaning either all provided values are stored or none at all.

Similarly to INSERT, UPDATE statement happening concurrently at different cluster nodes proceed without coordination. Cell values supplied by a statement with the highest timestamp will prevail. If two UPDATE statements or UPDATE and INSERT statements have the same timestamp, a conflict resolution algorithm determines which cells prevails (see :ref:update ordering <update-ordering>).

Regarding the :token:assignment:

• c = c + 3 is used to increment/decrement counters. The column name after the '=' sign must be the same as the one before the '=' sign. Note that increment/decrement is only allowed on counters, and are the only update operations allowed on counters. See the section on :ref:counters <counters> for details.
• id = id + <some-collection> and id[value1] = value2 are for collections, see the :ref:relevant section <collections> for details.
• id.field = 3 is for setting the value of a field on non-frozen user-defined types.

Please refer to the :ref:update parameters <update-parameters> section for more information on the :token:update_parameter.

.. _IF:

IF condition

It is, however, possible to use the conditions on some columns through ``IF``, in which case the row will not be updated
unless the conditions are met. Each such ``UPDATE`` gets a globally unique timestamp.
But, please note that using ``IF`` conditions will incur a non-negligible performance
cost (internally, Paxos will be used), so this should be used sparingly.


:doc:`Apache Cassandra Query Language (CQL) Reference </cql/index>`

.. include:: /rst_include/apache-copyrights.rst


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