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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