CREATE FUNCTION

Executes user-provided Java or Javascript code in SELECT, UPDATE, INSERT or provides a building block for user-defined aggregate. Functions are only available in the keyspace where they were created.

UDF supports Java generic methods or Javascript in the user provided codeblock. UDFs are susceptible to all of the normal issues that may occur with the chosen programming language. Safe guard against exceptions, such as null pointer exceptions, illegal arguments, or any other potential sources of problems. An exception during function execution results in the entire statement failing.

By default, the database does not allow UDFs. To enable, change the following settings in the cassandra.yaml and restart all nodes:

Set enable_user_defined_functions to true - allow users to create custom functions. Only Java is allowed in codeblocks if enable_scripted_user_defined_functions is false.
(Optional ) Set enable_scripted_user_defined_functions to true - allow function codeblocks to use Javascript.
(Optional) Set enable_user_defined_functions_threads to false to allow functions in GROUP BY clauses.

Synopsis

CREATE [ OR REPLACE ] FUNCTION [ IF NOT EXISTS ] [<keyspace_name>]<function_name> (<argument_list> [ , ... ])
  ( CALLED | RETURNS NULL ) ON NULL INPUT RETURNS <type>
  [ DETERMINISTIC ]
  [ MONOTONIC [ ON <argument_name> ] ]
  LANGUAGE ( java | javascript ) AS $$ <code_block> $$ ;

Syntax legend

Legend
Syntax conventions	Description
UPPERCASE	Literal keyword.
Lowercase	Not literal.
`< >`	Variable value. Replace with a user-defined value.
`[]`	Optional. Square brackets (`[]`) surround optional command arguments. Do not type the square brackets.
`( )`	Group. Parentheses ( `( )` ) identify a group to choose from. Do not type the parentheses.
`\|`	Or. A vertical bar (`\|`) separates alternative elements. Type any one of the elements. Do not type the vertical bar.
`...`	Repeatable. An ellipsis ( `...` ) indicates that you can repeat the syntax element as often as required.
`'<Literal string>'`	Single quotation (`'`) marks must surround literal strings in CQL statements. Use single quotation marks to preserve upper case.
`{ <key> : <value> }`	Map collection. Braces (`{ }`) enclose map collections or key value pairs. A colon separates the key and the value.
`<datatype2`	Set, list, map, or tuple. Angle brackets ( `< >` ) enclose data types in a set, list, map, or tuple. Separate the data types with a comma.
`<cql_statement>;`	End CQL statement. A semicolon (`;`) terminates all CQL statements.
`[--]`	Separate the command line options from the command arguments with two hyphens ( `--` ). This syntax is useful when arguments might be mistaken for command line options.
`' <<schema\> ... </schema\>> '`	Search CQL only: Single quotation marks (`'`) surround an entire XML schema declaration.
`@<xml_entity>='<xml_entity_type>'`	Search CQL only: Identify the entity and literal value to overwrite the XML element in the schema and solrConfig files.

<function_name>: Specify a keyspace-qualified function name. Names must start with a letter or number. To preserve case, enclose the name in double-quotes.
OR REPLACE: Overwrite the function, if one already exists with the same name.

Cannot be used with the IF NOT EXISTS option.

IF NOT EXISTS

Performs no operation and suppresses the error message if a function with the same name already exists.

argument_list

Comma separated list of arguments with data types passed to the code block for processing:

<arg_name> <cql_type> [,...]

In the list, specify an argument name followed by the CQL data type.

For requests, an argument value can be read from a column with the corresponding data type or manually entered (literal).

CALLED ON NULL INPUT

Executes the user-provided code block even if the input value is null or missing.

RETURNS NULL ON NULL INPUT

Does not execute the user-provided code block on null values; returns null.

RETURNS <cql_data_type>

Map the expected output from the code block to a compatible CQL data type.

DETERMINISTIC

Specify for functions that always returns the same output for a certain input. For example, toJson() is a deterministic function, while now() and currentDate() are not.

Default: false (non-deterministic).

GROUP BY only supports functions that are both deterministic and monotonic.

MONOTONIC [ ON <argument_name> ]: All arguments or the specified argument are monotonic if they are either entirely non-increasing or non-decreasing.

GROUP BY only supports functions that are both deterministic and monotonic.

LANGUAGE <language_name>

Supported types are java or javascript.

When https://docs.datastax.com/en/dse/6.8/dse-admin/datastax_enterprise/config/configCassandra_yaml.html#configCassandra_yamlenable_scripted_user_defined_functions[enable_scripted_user_defined_functions] is false and https://docs.datastax.com/en/dse/6.8/dse-admin/datastax_enterprise/config/configCassandra_yaml.html#configCassandra_yamlenable_user_defined_functions[enable_user_defined_functions] is true, Java is the only supported language.

'<code_block>' | $$ <code_block> $$

Enclose the code block in single quotes or if the code block contains any special characters enclose it in double dollar signs ($$). The code is wrapped as a function and applied to the target variables.

Examples

Use Java to create FLOG function

Overwrite or create the fLog function that computes the logarithm of an input value. CALLED ON NULL INPUT ensures that the function will always be executed.

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 $$ return Double.valueOf(Math.log(input.doubleValue())); $$;

Use Javascript to create SQL-like LEFT function

Create a function that returns the first <N> characters from a text field in Javascript. RETURNS NULL ON NULL INPUT ensures that if the input value is null then the function is not executed.

CREATE OR REPLACE FUNCTION cycling.left (column text, num int) 
  RETURNS NULL ON NULL INPUT 
  RETURNS text 
  LANGUAGE javascript AS $$ column.substring(0, num) $$;

Results

CREATE FUNCTION cycling.left(column text, num int)
    RETURNS NULL ON NULL INPUT
    RETURNS text
    LANGUAGE javascript
    AS $$ column.substring(0, num) $$;

Use the function in requests:

SELECT left(firstname, 1), lastname FROM cycling.cyclist_name;

Results

 cycling.left(firstname, 1) | lastname
----------------------------+-----------------
                          A |           FRAME
                       null |        MATTHEWS
                       null |             VOS
                          P |       TIRALONGO
                          M |             VOS
                          S |      KRUIKSWIJK
                          A | VAN DER BREGGEN

(7 rows)

CREATE FUNCTION

Synopsis

Examples

Use Java to create FLOG function

Use Javascript to create SQL-like LEFT function

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