Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/3510#discussion_r21128184
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercion.scala
---
@@ -219,6 +219,27 @@ trait HiveTypeCoercion {
if (b.right.dataType == widestType) b.right else
Cast(b.right, widestType)
b.makeCopy(Array(newLeft, newRight))
}.getOrElse(b) // If there is no applicable conversion, leave
expression unchanged.
+
+ case c @ Coalesce(exps) =>
+ val valueTypes = exps.map (_.dataType)
+ if (valueTypes.distinct.size > 1) {
+ val commonType = valueTypes.reduce { (v1, v2) =>
+ // When a string is found on one side, make the other side a
string too.
+ if (v1 == StringType || v2 == StringType) {
+ StringType
--- End diff --
I agree that we should probably add a bunch more tests to make sure that we
are doing the type coercion correctly here.
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