Create a user-defined function (UDF)

Write custom functions using Java or JavaScript to use in SELECT, INSERT, and UPDATE statements or as a building block for a user-defined aggregate (UDA). Functions are only available within the keyspace where it is defined. To preserve fast performance, use user-defined functions for short computations, and create Java UDFs instead of Javascript UDFs.

You can define functions that are executed against data stored in a table as part of a query result. The function must be created prior to its use in a SELECT statement. The function is performed on each row of the table.

Prerequisites

Keyspace exists

By default, the ability to add user-defined functions is disabled. To enable, change the following settings in the cassandra.yaml file:

Java: Set enable_user_defined_functions to true.
JavaScript (in addition to Java): Set enable_scripted_user_defined_functions to true.

Create a function, specifying the data type of the returned value, the language, and the actual code of the function to be performed. The following function, fLog(), computes the logarithmic value of each input. It is a built-in java function and used to generate linear plots of non-linear data.

For this example, it presents a simple math function to show the capabilities of user-defined functions.

CREATE OR REPLACE FUNCTION cycling.flog ( input double ) 
  CALLED ON NULL INPUT 
  RETURNS double 
  LANGUAGE java AS 
    $$ return Double.valueOf(Math.log(input.doubleValue())); $$ 
;

Results

CREATE FUNCTION cycling.flog(input double)
    CALLED ON NULL INPUT
    RETURNS double
    LANGUAGE java
    AS $$ return Double.valueOf(Math.log(input.doubleValue())); $$;

Actions when the input from the target column is null:
- CALLED ON NULL INPUT ensures the function always executes when called.
- RETURNS NULL ON NULL INPUT ensures the function always returns NULL if any of the input arguments are NULL.
RETURNS defines the CQL data type of the value returned by the function.
A function can be replaced with a different function if OR REPLACE is used as shown in the example above. Optionally, the IF NOT EXISTS keywords can be used to create the function only if another function with the same signature does not exist in the keyspace. OR REPLACE and IF NOT EXISTS cannot be used in the same command.

Create a user-defined function (UDF)

Prerequisites

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