Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/4057#discussion_r23717159
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercion.scala
---
@@ -503,6 +503,18 @@ trait HiveTypeCoercion {
// Hive lets you do aggregation of timestamps... for some reason
case Sum(e @ TimestampType()) => Sum(Cast(e, DoubleType))
case Average(e @ TimestampType()) => Average(Cast(e, DoubleType))
+
+ case Coalesce(es) if es.map(_.dataType).distinct.size > 1 =>
+ val dt: Option[DataType] = Some(NullType)
+ val rt = es.map(_.dataType).foldLeft(dt)((r, c) => if (r != None) {
+ findTightestCommonType(r.get, c)
+ } else {
+ None
+ })
+ rt match {
+ case Some(ddt) => Coalesce(es.map(Cast(_, ddt)))
+ case None => sys.error("Cannot do type coercion over coalesce")
--- End diff --
Seems it will be good to also let users know the data types of those
expressions in the `Coalesce`. Also, maybe `type coercion` is not very user
friendly. How about "Could not determine the return type of Coalesce" and then
provide the types of expressions?
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