Github user concretevitamin commented on a diff in the pull request:
https://github.com/apache/spark/pull/1785#discussion_r15828596
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercion.scala
---
@@ -336,28 +338,33 @@ trait HiveTypeCoercion {
}
/**
- * Ensures that NullType gets casted to some other types under certain
circumstances.
+ * Coerces the type of different branches of a CASE WHEN statement to a
common type.
*/
- object CastNulls extends Rule[LogicalPlan] {
+ object CaseWhenCoercion extends Rule[LogicalPlan] with TypeWidening {
def apply(plan: LogicalPlan): LogicalPlan = plan
transformAllExpressions {
- case cw @ CaseWhen(branches) =>
+ case cw @ CaseWhen(branches) if !cw.resolved &&
!branches.exists(!_.resolved) =>
val valueTypes = branches.sliding(2, 2).map {
- case Seq(_, value) if value.resolved => Some(value.dataType)
- case Seq(elseVal) if elseVal.resolved => Some(elseVal.dataType)
- case _ => None
+ case Seq(_, value) => value.dataType
+ case Seq(elseVal) => elseVal.dataType
}.toSeq
- if (valueTypes.distinct.size == 2 && valueTypes.exists(_ ==
Some(NullType))) {
- val otherType = valueTypes.filterNot(_ == Some(NullType))(0).get
+
+ logDebug(s"Input values for null casting
${valueTypes.mkString(",")}")
+
+ if (valueTypes.distinct.size > 1) {
+ val commonType = valueTypes.reduce { (v1, v2) =>
+ findTightestCommonType(v1, v2)
+ .getOrElse(sys.error(s"Invalid types in CASE WHEN. $v1,
$v2"))
--- End diff --
Perhaps "Value types in CASE WHEN must be the same, or can be coerced to a
tightest upper bound." to be more precise about the semantics, in case users
run into this.
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