Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/21074#discussion_r182100748
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
---
@@ -176,16 +176,16 @@ object TypeCoercion {
}
private def findWiderCommonType(types: Seq[DataType]): Option[DataType]
= {
- types.foldLeft[Option[DataType]](Some(NullType))((r, c) => r match {
- case Some(d) => findWiderTypeForTwo(d, c)
- // Currently we find the wider common type by comparing the two
types from left to right,
- // this can be a problem when you have two data types which don't
have a common type but each
- // can be promoted to StringType. For instance, (TimestampType,
IntegerType, StringType)
- // should have StringType as the wider common type.
- case None if types.exists(_ == StringType) &&
- types.forall(stringPromotion(_, StringType).nonEmpty) =>
Some(StringType)
- case _ => 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 when each of the types is
StringType or can be
--- End diff --
`This is only a problem for StringType`
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