dilipbiswal commented on a change in pull request #25894:
[SPARK-28793][DOC][SQL] Document CREATE FUNCTION in SQL Reference
URL: https://github.com/apache/spark/pull/25894#discussion_r334331187
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File path: docs/sql-ref-syntax-ddl-create-function.md
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@@ -19,4 +19,154 @@ license: |
limitations under the License.
---
-**This page is under construction**
+### Description
+The `CREATE FUNCTION` statement is used to create a temporary or permanent
function
+in Spark. 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 users to create custom user defined scalar and
+aggregate functions using Scala, Python and Java APIs. Please refer to
+[scalar_functions](sql-getting-started.html#scalar-functions) and
+[aggregate functions](sql-getting-started#aggregations) for more information.
+
+### Syntax
+{% highlight sql %}
+CREATE [ OR REPLACE ] [ TEMPORARY ] FUNCTION [ IF NOT EXISTS ]
+ function_name AS class_name [ resource_locations ]
+{% endhighlight %}
+
+### Parameters
+<dl>
+ <dt><code><em>OR REPLACE</em></code></dt>
+ <dd>
+ If specified, the resources for 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 <code>IF NOT EXISTS</code> and can not
+ be specified together.
+ </dd>
+ <dt><code><em>TEMPORARY</em></code></dt>
+ <dd>
+ 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.
+ </dd>
+ <dt><code><em>IF NOT EXISTS</em></code></dt>
+ <dd>
+ 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 <code> OR
REPLACE</code>
+ and can not be specified together.
+ </dd>
+ <dt><code><em>function_name</em></code></dt>
+ <dd>
+ Specifies a name of funnction to be created. The function name may be
+ optionally qualified with a database name. <br><br>
+ <b>Syntax:</b>
+ <code>
+ [database_name.]function_name
+ </code>
+ </dd>
+ <dt><code><em>class_name</em></code></dt>
+ <dd>
+ Specifies the name of the class that provides the implementation for
function to be created.
+ The implementing class should extend from one of the base classes as
follows:
+ <ul>
+ <li>Should extend <code>UDF</code> or <code>UDAF</code> in
<code>org.apache.hadoop.hive.ql.exec</code> package.</li>
+ <li>Should extend <code>AbstractGenericUDAFResolver</code>,
<code>GenericUDF</code>, or
+ <code>GenericUDTF</code> in
<code>org.apache.hadoop.hive.ql.udf.generic</code> package.</li>
+ <li>Should extend <code>UserDefinedAggregateFunction</code> in
<code>org.apache.spark.sql.expressions</code> package.</li>
+ </ul>
+ </dd>
+ <dt><code><em>resource_locations</em></code></dt>
+ <dd>
+ Specifies the list of resources that contain the implementation of the
function
+ along with its dependencies. <br><br>
+ <b>Syntax:</b>
+ <code>
+ USING { { (JAR | FILE ) resource_uri} , ...}
+ </code>
+ </dd>
+</dl>
+
+### Examples
+{% highlight sql %}
+-- 1. Create a simple UDF `SimpleUdf` that adds 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.
+-- Please note that the temporary function does not have a qualified
+-- database associated with it.
+SHOW USER FUNCTIONS;
+ +------------------+
+ | function|
+ +------------------+
+ |default.simple_udf|
+ | simple_temp_udf|
+ +------------------+
+
+-- 1. Mofify `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|
++---------------------+
+
+{% endhighlight %}
+
+### Related statements
+- [SHOW FUNCTIONS](sql-ref-syntax-aux-show-functions.html)
+- [DESCRIBE FUNCTION](sql-ref-syntax-aux-describe-function.html)
+- [DESCRIBE FUNCTION](sql-ref-syntax-aux-describe-function.html)
Review comment:
@gatorsmile oops.. thanks for catching it. Will fix.
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