Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/6754#discussion_r32278918
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercion.scala
---
@@ -653,6 +663,26 @@ trait HiveTypeCoercion {
}
/**
+ * Coerces the type of different branches of If statement to a common
type.
+ */
+ object IfCoercion extends Rule[LogicalPlan] {
+ def apply(plan: LogicalPlan): LogicalPlan = plan
transformAllExpressions {
+ // Find tightest common type for If, if the true value and false
value have different types.
+ case i @ If(pred, left, right) if left.dataType != right.dataType =>
+ findTightestCommonTypeToString(left.dataType, right.dataType).map
{ widestType =>
+ val newLeft = if (left.dataType == widestType) left else
Cast(left, widestType)
+ val newRight = if (right.dataType == widestType) right else
Cast(right, widestType)
+ i.makeCopy(Array(pred, newLeft, newRight))
+ }.getOrElse(i) // If there is no applicable conversion, leave
expression unchanged.
+
+ // Convert If(null literal, _, _) into boolean type.
+ // In the optimizer, we should short-circuit this directly into
false value.
+ case i @ If(pred, left, right) if pred.dataType == NullType =>
+ i.makeCopy(Array(Literal.create(null, BooleanType), left, right))
--- End diff --
Why this special case? Also, I'd just use `If`instead of makeCopy here and
above. Make copy is nice when you are matching on different but structurally
similar expression, but looses compile time checks for arguments.
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