# UPDATE Updating a row is done using an `UPDATE` statement: ```cql 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: ```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 `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 [update ordering](https://docs.scylladb.com/manual/master/cql/dml.md#update-ordering)). Regarding the `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 [counters](https://docs.scylladb.com/manual/master/cql/types.md#counters) for details. - `id = id + ` and `id[value1] = value2` are for collections, see the [relevant section](https://docs.scylladb.com/manual/master/cql/types.md#collections) for details. - `id.field = 3` is for setting the value of a field on non-frozen user-defined types. Please refer to the [update parameters](https://docs.scylladb.com/manual/master/cql/dml.md#update-parameters) section for more information on the `update_parameter`. ## 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. [Apache Cassandra Query Language (CQL) Reference](https://docs.scylladb.com/manual/master/cql/index.md) Copyright © 2016, The Apache Software Foundation. Apache®, Apache Cassandra®, Cassandra®, the Apache feather logo and the Apache Cassandra® Eye logo are either registered trademarks or trademarks of the Apache Software Foundation in the United States and/or other countries. No endorsement by The Apache Software Foundation is implied by the use of these marks.