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From chenghao-intel <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-4856] [SQL] NullType instead of StringT...
Date Wed, 17 Dec 2014 01:00:43 GMT
Github user chenghao-intel commented on a diff in the pull request:

    https://github.com/apache/spark/pull/3708#discussion_r21945992
  
    --- Diff: sql/core/src/main/scala/org/apache/spark/sql/json/JsonRDD.scala ---
    @@ -263,6 +263,8 @@ private[sql] object JsonRDD extends Logging {
             val elementType = typeOfArray(array)
             buildKeyPathForInnerStructs(array, elementType) :+ (key, elementType)
           }
    +      // we couldn't tell what the type is if the value is null or empty string
    +      case (key: String, value) if value == "" || value == null => (key, NullType)
:: Nil
    --- End diff --
    
    I've updated the unit test, which probably make more sense.
    
    In some cases (as shown in the unit test), `""` is equivalent to `null` for struct type,
so we'd better not to say "it's MUST be `StringType` if we meet an empty string".
    
    In the meantime, the `NullType` is the `minimum` data type, and it can be promoted to
any other data type in `JsonRDD` (e.g. promote to StructType), however, it's impossible to
promote a `StringType` to `StructType`.
    
    It's safe to make it as `NullType` here, as we can promote it as `StringType` in the last
promote rules, see https://github.com/chenghao-intel/spark/blob/json/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala#L231


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