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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept rev="1.2" id="drop_function">

  <title>DROP FUNCTION Statement</title>
  <titlealts audience="PDF"><navtitle>DROP FUNCTION</navtitle></titlealts>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="SQL"/>
      <data name="Category" value="DDL"/>
      <data name="Category" value="Impala Functions"/>
      <data name="Category" value="UDFs"/>
      <data name="Category" value="Schemas"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Data Analysts"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      <indexterm audience="hidden">DROP FUNCTION statement</indexterm>
      Removes a user-defined function (UDF), so that it is not available for execution during Impala
      <codeph>SELECT</codeph> or <codeph>INSERT</codeph> operations.
    </p>

    <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

    <p>
      To drop C++ UDFs and UDAs:
    </p>

<codeblock>DROP [AGGREGATE] FUNCTION [IF EXISTS] [<varname>db_name</varname>.]<varname>function_name</varname>(<varname>type</varname>[, <varname>type</varname>...])</codeblock>

    <note rev="2.5.0 IMPALA-2843">
      <p rev="2.5.0 IMPALA-2843">
        The preceding syntax, which includes the function signature, also applies to Java UDFs that were created
        using the corresponding <codeph>CREATE FUNCTION</codeph> syntax that includes the argument and return types.
        After upgrading to <keyword keyref="impala25_full"/> or higher, consider re-creating all Java UDFs with the
        <codeph>CREATE FUNCTION</codeph> 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.
      </p>
    </note>

    <p rev="2.5.0 IMPALA-2843">
      To drop Java UDFs (created using the <codeph>CREATE FUNCTION</codeph> syntax with no function signature):
    </p>

<codeblock rev="2.5.0">DROP FUNCTION [IF EXISTS] [<varname>db_name</varname>.]<varname>function_name</varname></codeblock>

<!--
Examples:
CREATE FUNCTION IF NOT EXISTS foo location '/path/to/jar' SYMBOL='TestUdf';
CREATE FUNCTION bar location '/path/to/jar' SYMBOL='TestUdf2';
DROP FUNCTION foo;
DROP FUNCTION IF EXISTS bar;
-->

    <p conref="../shared/impala_common.xml#common/ddl_blurb"/>

    <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>

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

    <p conref="../shared/impala_common.xml#common/restrictions_blurb"/>

    <p conref="../shared/impala_common.xml#common/udf_persistence_restriction"/>

    <p conref="../shared/impala_common.xml#common/cancel_blurb_no"/>

    <p conref="../shared/impala_common.xml#common/permissions_blurb"/>
    <p rev="">
      The user ID that the <cmdname>impalad</cmdname> daemon runs under,
      typically the <codeph>impala</codeph> 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.
    </p>

    <p conref="../shared/impala_common.xml#common/example_blurb"/>
    <p rev="2.5.0 IMPALA-2843">
      The following example shows how to drop Java functions created with the signatureless
      <codeph>CREATE FUNCTION</codeph> syntax in <keyword keyref="impala25_full"/> and higher.
      Issuing <codeph>DROP FUNCTION <varname>function_name</varname></codeph> removes all the
      overloaded functions under that name.
      (See <xref href="impala_create_function.xml#create_function"/> for a longer example
      showing how to set up such functions in the first place.)
    </p>
<codeblock rev="2.5.0 IMPALA-2843">
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          |
...
</codeblock>

    <p conref="../shared/impala_common.xml#common/related_info"/>

    <p>
      <xref href="impala_udf.xml#udfs"/>, <xref href="impala_create_function.xml#create_function"/>
    </p>
  </conbody>
</concept>