Github user dongjoon-hyun commented on a diff in the pull request:
https://github.com/apache/spark/pull/18460#discussion_r125959164
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
---
@@ -144,6 +145,12 @@ object TypeCoercion {
.orElse((t1, t2) match {
case (ArrayType(et1, containsNull1), ArrayType(et2,
containsNull2)) =>
findWiderTypeForTwo(et1, et2).map(ArrayType(_, containsNull1 ||
containsNull2))
+ case (st1 @ StructType(fields1), st2 @ StructType(fields2)) if
st1.sameType(st2) =>
+ Some(StructType(fields1.zip(fields2).map { case (sf1, sf2) =>
+ val name = if (sf1.name == sf2.name) sf1.name else
sf1.name.toLowerCase(Locale.ROOT)
+ val dataType = findWiderTypeForTwo(sf1.dataType,
sf2.dataType).get
--- End diff --
Sorry for making this confused.
I added the comment in [the
test](https://github.com/apache/spark/pull/18460/files/d3a9f73c1a19818bf9970d1102fc1b8d1cf0effa#diff-01ecdd038c5c2f53f38118912210fef8R443).
```
StructType does not widen the types, but supports case-sensitive options.
```
This line are guarded by `if st1.sameType(st2)`. So, we always have the
same `dataType`.
The reason to use `findWiderTypeForTwo` is to get the final nested complex
type with the new nullability.
Also, this function is `findWiderTypeForTwo`.
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