Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/6551#discussion_r31798086
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercion.scala
---
@@ -59,6 +59,42 @@ object HiveTypeCoercion {
}
/**
+ * Implicit promote the DataType to StringType if
+ * one of the data type in (dt1, dt2) is StringType, and the other is
not either
+ * BooleanType or BinaryType, the TightestCommonType should be StringType
+ * eg: 1. CaseWhenLike case when ... then dt1 else dt2 end
+ * 2. Coalesce(null, dt1, dt2)
+
+ */
+ val promoteToStringTypeOfTwo: (DataType, DataType) => Option[DataType] =
{
+ case (t1: StringType, t2: DataType) if (t2 != BinaryType && t2 !=
BooleanType) =>
+ Some(StringType)
+
+ case (t1: DataType, t2: StringType) if (t1 != BinaryType && t1 !=
BooleanType) =>
+ Some(StringType)
+
+ case _ => None
+ }
+
+ /**
+ * Find the tightest common type of a set of types by continuously
applying
+ * `findTightestCommonTypeOfTwo` on these types.
+ */
+ private def findTightestCommonTypeAndTryPromoteToString(types:
Seq[DataType]) = {
+ types.foldLeft[Option[DataType]](Some(NullType))((r, c) => r match {
+ case None => None
+ case Some(d) =>
+ val dt = findTightestCommonTypeOfTwo(d, c)
+ if (dt == None) {
+ promoteToStringTypeOfTwo(d, c)
+ } else {
+ dt
--- End diff --
`findTightestCommonTypeOfTwo(d, c).orElse(promoteToStringTypeOfTwo(d, c))`?
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