[GitHub] spark pull request #18576: [SPARK-21351][SQL] Update nullability based on ch...

[maropu <gi...@git.apache.org>]

Github user maropu commented on a diff in the pull request:

    https://github.com/apache/spark/pull/18576#discussion_r131573104
  
    --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/basicPhysicalOperators.scala ---
    @@ -94,27 +94,14 @@ case class FilterExec(condition: Expression, child: SparkPlan)
         case _ => false
       }
     
    -  // If one expression and its children are null intolerant, it is null intolerant.
    -  private def isNullIntolerant(expr: Expression): Boolean = expr match {
    -    case e: NullIntolerant => e.children.forall(isNullIntolerant)
    -    case _ => false
    -  }
    -
    -  // The columns that will filtered out by `IsNotNull` could be considered as not nullable.
    -  private val notNullAttributes = notNullPreds.flatMap(_.references).distinct.map(_.exprId)
    -
       // Mark this as empty. We'll evaluate the input during doConsume(). We don't want to evaluate
       // all the variables at the beginning to take advantage of short circuiting.
       override def usedInputs: AttributeSet = AttributeSet.empty
     
    +  // Since some plan rewrite rules (e.g., python.ExtractPythonUDFs) possibly change child's output
    +  // from optimized logical plans, we need to adjust the filter's output here.
       override def output: Seq[Attribute] = {
    -    child.output.map { a =>
    -      if (a.nullable && notNullAttributes.contains(a.exprId)) {
    -        a.withNullability(false)
    -      } else {
    -        a
    -      }
    -    }
    +    child.output.map { attr => outputAttrs.find(_.exprId == attr.exprId).getOrElse(attr) }
       }
    --- End diff --
    
    I simply tried to drop updating nullability and reuse output attributes `outputAttrs` in an optimized logical plan here though, some python tests failed (all the scala tests passed). I checked and I found this; in the planner path of python, we have some cases changing operator's output from the optimized logical plan to a physical plan.
    For example;
    ```
    sql("""SELECT strlen(a) FROM test WHERE strlen(a) > 1""")
    
    // pyspark
    >>> spark.sql("SELECT strlen(a) FROM test WHERE strlen(a) > 1").explain(True)
    ...
    == Optimized Logical Plan ==
    Project [strlen(a#0) AS strlen(a)#30]
    +- Filter (strlen(a#0) > 1)
       +- LogicalRDD [a#0]
    
    == Physical Plan ==
    *Project [pythonUDF0#34 AS strlen(a)#30]
    +- BatchEvalPython [strlen(a#0)], [a#0, pythonUDF0#34]
       +- *Filter (pythonUDF0#33 > 1), [a#0]
          +- BatchEvalPython [strlen(a#0)], [a#0, pythonUDF0#33]
             +- Scan ExistingRDD[a#0]
    ```
    So, I added code to check a difference between `outputAttrs` and `child.output`.
    Could you give me insight on this? @gatorsmile 


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