Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/13290#discussion_r64686215
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
---
@@ -1448,6 +1450,37 @@ class Analyzer(
}
/**
+ * Fixes nullability of Attributes in a resolved LogicalPlan by using
the nullability of
+ * corresponding Attributes of its children output Attributes. This step
is needed because
+ * users can use a resolved AttributeReference in the Dataset API and
outer joins
+ * can change the nullability of an AttribtueReference. Without the fix,
a nullable column's
+ * nullable field can be actually set as non-nullable, which cause
illegal optimization
+ * (e.g., NULL propagation) and wrong answers.
+ * See SPARK-13484 and SPARK-13801 for the concrete queries of this case.
+ */
+ object FixNullability extends Rule[LogicalPlan] {
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
+ case q: LogicalPlan if q.resolved =>
+ val childrenOutput = q.children.flatMap(c =>
c.output).groupBy(_.exprId).flatMap {
--- End diff --
Yea. This version tries to fix the nullability for the entire query plan
tree because I think it is possible to hit this problem in other cases when
using Dataset API.
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