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From cloud-fan <...@git.apache.org>
Subject [GitHub] spark pull request #17848: [SPARK-20586] [SQL] Add deterministic to ScalaUDF...
Date Thu, 20 Jul 2017 07:31:30 GMT
Github user cloud-fan commented on a diff in the pull request:

    https://github.com/apache/spark/pull/17848#discussion_r128443096
  
    --- Diff: sql/core/src/main/scala/org/apache/spark/sql/UDFRegistration.scala ---
    @@ -79,8 +79,15 @@ class UDFRegistration private[sql] (functionRegistry: FunctionRegistry)
extends
       }
     
       /**
    -   * Register a user-defined function (UDF), for a UDF that's already defined using the
DataFrame
    -   * API (i.e. of type UserDefinedFunction).
    +   * Registers a user-defined function (UDF), for a UDF that's already defined using
the Dataset
    +   * API (i.e. of type UserDefinedFunction). To change a UDF to nondeterministic, call
the API
    +   * `UserDefinedFunction.asNondeterministic()`.
    --- End diff --
    
    a good example will be
    ```
    val foo = udf(() => { "hello" })
    spark.udf.register("stringContant", foo.asNonNullable())
    ```
    Although the return type of the UDF is `String` and is nullable, but we know that this
UDF will never return null.


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