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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