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CREATE FUNCTION (External)

  • Άρθρο

Applies to: check marked yes Databricks Runtime

Creates a temporary or permanent external function. Temporary functions are scoped at a session level where as permanent functions are created in the persistent catalog and are made available to all sessions. The resources specified in the USING clause are made available to all executors when they are executed for the first time.

In addition to the SQL interface, Spark allows you to create custom user defined scalar and aggregate functions using Scala, Python, and Java APIs. See External user-defined scalar functions (UDFs) and User-defined aggregate functions (UDAFs) for more information.

Syntax

CREATE [ OR REPLACE ] [ TEMPORARY ] FUNCTION [ IF NOT EXISTS ]
    function_name AS class_name [ resource_locations ]

Parameters

  • OR REPLACE

    If specified, the resources for the function are reloaded. This is mainly useful to pick up any changes made to the implementation of the function. This parameter is mutually exclusive to IF NOT EXISTS and cannot be specified together.

  • TEMPORARY

    Indicates the scope of function being created. When TEMPORARY is specified, the created function is valid and visible in the current session. No persistent entry is made in the catalog for these kind of functions.

  • IF NOT EXISTS

    If specified, creates the function only when it does not exist. The creation of function succeeds (no error is thrown) if the specified function already exists in the system. This parameter is mutually exclusive to OR REPLACE and cannot be specified together.

  • function_name

    A name for the function. The function name may be optionally qualified with a schema name.

    Functions created in hive_metastore can only contain alphanumeric ASCII characters and underscores.

  • class_name

    The name of the class that provides the implementation for function to be created. The implementing class should extend one of the base classes as follows:

    • Should extend UDF or UDAF in org.apache.hadoop.hive.ql.exec package.
    • Should extend AbstractGenericUDAFResolver, GenericUDF, or GenericUDTF in org.apache.hadoop.hive.ql.udf.generic package.
    • Should extend UserDefinedAggregateFunction in org.apache.spark.sql.expressions package.

  • resource_locations

    The list of resources that contain the implementation of the function along with its dependencies.

    Syntax: USING { { (JAR | FILE | ARCHIVE) resource_uri } , ... }

Examples

-- 1. Create a simple UDF `SimpleUdf` that increments the supplied integral value by 10.
--    import org.apache.hadoop.hive.ql.exec.UDF;
--    public class SimpleUdf extends UDF {
--      public int evaluate(int value) {
--        return value + 10;
--      }
--    }
-- 2. Compile and place it in a JAR file called `SimpleUdf.jar` in /tmp.

-- Create a table called `test` and insert two rows.
> CREATE TABLE test(c1 INT);
> INSERT INTO test VALUES (1), (2);

-- Create a permanent function called `simple_udf`.
> CREATE FUNCTION simple_udf AS 'SimpleUdf'
    USING JAR '/tmp/SimpleUdf.jar';

-- Verify that the function is in the registry.
> SHOW USER FUNCTIONS;
           function
 ------------------
 default.simple_udf

-- Invoke the function. Every selected value should be incremented by 10.
> SELECT simple_udf(c1) AS function_return_value FROM t1;
 function_return_value
 ---------------------
                    11
                    12

-- Created a temporary function.
> CREATE TEMPORARY FUNCTION simple_temp_udf AS 'SimpleUdf'
    USING JAR '/tmp/SimpleUdf.jar';

-- Verify that the newly created temporary function is in the registry.
-- The temporary function does not have a qualified
-- schema associated with it.
> SHOW USER FUNCTIONS;
           function
 ------------------
 default.simple_udf
    simple_temp_udf

-- 1. Modify `SimpleUdf`'s implementation to add supplied integral value by 20.
--    import org.apache.hadoop.hive.ql.exec.UDF;

--    public class SimpleUdfR extends UDF {
--      public int evaluate(int value) {
--        return value + 20;
--      }
--    }
-- 2. Compile and place it in a jar file called `SimpleUdfR.jar` in /tmp.

-- Replace the implementation of `simple_udf`
> CREATE OR REPLACE FUNCTION simple_udf AS 'SimpleUdfR'
    USING JAR '/tmp/SimpleUdfR.jar';

-- Invoke the function. Every selected value should be incremented by 20.
> SELECT simple_udf(c1) AS function_return_value FROM t1;
 function_return_value
 ---------------------
                    21
                    22