DROP FUNCTION Statement

Removes a user-defined function (UDF), so that it is not available for execution during Impala SELECT or INSERT operations.

Syntax:

To drop C++ UDFs and UDAs:

DROP [AGGREGATE] FUNCTION [IF EXISTS] [db_name.]function_name(type[, type...])

Note:

The preceding syntax, which includes the function signature, also applies to Java UDFs that were created using the corresponding CREATE FUNCTION syntax that includes the argument and return types. After upgrading to Impala 2.5 or higher, consider re-creating all Java UDFs with the CREATE FUNCTION syntax that does not include the function signature. Java UDFs created this way are now persisted in the metastore database and do not need to be re-created after an Impala restart.

To drop Java UDFs (created using the CREATE FUNCTION syntax with no function signature):

DROP FUNCTION [IF EXISTS] [db_name.]function_name

Statement type: DDL

Usage notes:

Because the same function name could be overloaded with different argument signatures, you specify the argument types to identify the exact function to drop.

Restrictions:

In Impala 2.5 and higher, Impala UDFs and UDAs written in C++ are persisted in the metastore database. Java UDFs are also persisted, if they were created with the new CREATE FUNCTION syntax for Java UDFs, where the Java function argument and return types are omitted. Java-based UDFs created with the old CREATE FUNCTION syntax do not persist across restarts because they are held in the memory of the catalogd daemon. Until you re-create such Java UDFs using the new CREATE FUNCTION syntax, you must reload those Java-based UDFs by running the original CREATE FUNCTION statements again each time you restart the catalogd daemon. Prior to Impala 2.5 the requirement to reload functions after a restart applied to both C++ and Java functions.

Cancellation: Cannot be cancelled.

HDFS permissions:

The user ID that the impalad daemon runs under, typically the impala user, does not need any particular HDFS permissions to perform this statement. All read and write operations are on the metastore database, not HDFS files and directories.

Examples:

The following example shows how to drop Java functions created with the signatureless CREATE FUNCTION syntax in Impala 2.5 and higher. Issuing DROP FUNCTION function_name removes all the overloaded functions under that name. (See CREATE FUNCTION Statement for a longer example showing how to set up such functions in the first place.)

create function my_func location '/user/impala/udfs/udf-examples.jar'
  symbol='org.apache.impala.TestUdf';
show functions;
+-------------+---------------------------------------+-------------+---------------+
| return type | signature                             | binary type | is persistent |
+-------------+---------------------------------------+-------------+---------------+
| BIGINT      | my_func(BIGINT)                       | JAVA        | true          |
| BOOLEAN     | my_func(BOOLEAN)                      | JAVA        | true          |
| BOOLEAN     | my_func(BOOLEAN, BOOLEAN)             | JAVA        | true          |
...
| BIGINT      | testudf(BIGINT)                       | JAVA        | true          |
| BOOLEAN     | testudf(BOOLEAN)                      | JAVA        | true          |
| BOOLEAN     | testudf(BOOLEAN, BOOLEAN)             | JAVA        | true          |
...
drop function my_func;
show functions;
+-------------+---------------------------------------+-------------+---------------+
| return type | signature                             | binary type | is persistent |
+-------------+---------------------------------------+-------------+---------------+
| BIGINT      | testudf(BIGINT)                       | JAVA        | true          |
| BOOLEAN     | testudf(BOOLEAN)                      | JAVA        | true          |
| BOOLEAN     | testudf(BOOLEAN, BOOLEAN)             | JAVA        | true          |
...

Related information:

User-Defined Functions (UDFs), CREATE FUNCTION Statement

Parent topic: Impala SQL Statements