[GitHub] spark pull request: [SPARK-11319][SQL] Making StructField's nullab...

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

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

    https://github.com/apache/spark/pull/11785#discussion_r62391024
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/types/StructField.scala ---
    @@ -24,7 +24,9 @@ import org.json4s.JsonDSL._
      * A field inside a StructType.
      * @param name The name of this field.
      * @param dataType The data type of this field.
    - * @param nullable Indicates if values of this field can be `null` values.
    + * @param nullable Indicates if values of this field can be `null` values. Note that this is ONLY A HINT to the 
    --- End diff --
    
    According to @marmbrus's [comment here](https://issues.apache.org/jira/browse/SPARK-11319?focusedCommentId=15014678&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15014678) this is actually much stronger than a hint:
    
    > Fair, this is **a contract with the optimizer that you will not produce null data**. If you are not certain you will not produce null values then set this to true.


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