Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/21074#discussion_r182458121
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
---
@@ -175,11 +175,27 @@ object TypeCoercion {
})
}
+ /**
+ * Whether the data type contains StringType.
+ */
+ def hasStringType(dt: DataType): Boolean = dt match {
+ case StringType => true
+ case ArrayType(et, _) => hasStringType(et)
+ // Add StructType if we support string promotion for struct fields in
the future.
+ case _ => false
+ }
+
private def findWiderCommonType(types: Seq[DataType]): Option[DataType]
= {
- types.foldLeft[Option[DataType]](Some(NullType))((r, c) => r match {
- case Some(d) => findWiderTypeForTwo(d, c)
- case None => None
- })
+ // findWiderTypeForTwo doesn't satisfy the associative law, i.e. (a op
b) op c may not equal
+ // to a op (b op c). This is only a problem for StringType. Excluding
StringType,
--- End diff --
`This is only a problem for StringType or nested StringType in ArrayType.
Excluding these types, ...`
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