Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/19977#discussion_r158327829
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
---
@@ -658,6 +660,30 @@ object TypeCoercion {
}
}
+ /**
+ * Coerces the types of [[Concat]] children to expected ones.
+ *
+ * If `spark.sql.function.concatBinaryAsString` is false and all
children types are binary,
+ * the expected types are binary. Otherwise, the expected ones are
strings.
+ */
+ case class ConcatCoercion(conf: SQLConf) extends TypeCoercionRule {
+ override protected def coerceTypes(
+ plan: LogicalPlan): LogicalPlan = plan transformExpressionsUp {
+ // Skip nodes if unresolved or empty children
+ case c @ Concat(children) if !c.childrenResolved || children.isEmpty
=> c
+
+ case c @ Concat(children) if !children.map(_.dataType).forall(_ ==
BinaryType) =>
+ val newChildren = children.map { e =>
+ ImplicitTypeCasts.implicitCast(e, StringType).getOrElse(e)
+ }
+ c.copy(children = newChildren)
+
+ case c @ Concat(children) if conf.concatBinaryAsString =>
+ val newChildren = children.map(Cast(_, StringType))
--- End diff --
also use `ImplicitTypeCasts.implicitCast` here?
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