[GitHub] spark pull request #18460: [SPARK-21247][SQL] Type comparision should respec...

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

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

    https://github.com/apache/spark/pull/18460#discussion_r143238804
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala ---
    @@ -100,6 +101,17 @@ object TypeCoercion {
         case (_: TimestampType, _: DateType) | (_: DateType, _: TimestampType) =>
           Some(TimestampType)
     
    +    case (t1 @ StructType(fields1), t2 @ StructType(fields2)) if t1.sameType(t2) =>
    +      Some(StructType(fields1.zip(fields2).map { case (f1, f2) =>
    +        // Since `t1.sameType(t2)` is true, two StructTypes have the same DataType
    +        // except `name` (in case of `spark.sql.caseSensitive=false`) and `nullable`.
    +        // - Different names: use a lower case name because findTightestCommonType is commutative.
    +        // - Different nullabilities: `nullable` is true iff one of them is nullable.
    +        val name = if (f1.name == f2.name) f1.name else f1.name.toLowerCase(Locale.ROOT)
    --- End diff --
    
    Why the output nested column name is lower case? Is Hive behaving like this?
    
    In addition, could you add one more test and check whether we also respect case sensitivity conf when we resolve the queries that contain the nested column in the references?


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