Github user gatorsmile commented on a diff in the pull request: https://github.com/apache/spark/pull/18460#discussion_r143906721 --- 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) + val dataType = findTightestCommonType(f1.dataType, f2.dataType).get + StructField(name, dataType, nullable = f1.nullable || f2.nullable) --- End diff -- See the example, ```Scala sql("SELECT 1 as a UNION ALL (SELECT 1 as A)").show() sql("SELECT 1 as A UNION ALL (SELECT 1 as a)").show() ```
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