Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/21704#discussion_r200110924
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala
---
@@ -2007,7 +2007,14 @@ case class Concat(children: Seq[Expression]) extends
Expression {
}
}
- override def dataType: DataType =
children.map(_.dataType).headOption.getOrElse(StringType)
+ override def dataType: DataType = {
+ val dataTypes = children.map(_.dataType)
+ dataTypes.headOption.map {
+ case ArrayType(et, _) =>
+ ArrayType(et,
dataTypes.exists(_.asInstanceOf[ArrayType].containsNull))
+ case dt => dt
+ }.getOrElse(StringType)
+ }
--- End diff --
> what about changing SimplifyCasts rule to start replacing Cast with a new
dummy cast expression that will hold only a target data type and won't perform
any casting?
This can work, but my point is we should not add the cast to change
`containsNull`, as it may not match the underlying child expression and
generates unnecessary null check code.
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