Github user chenghao-intel commented on a diff in the pull request:
https://github.com/apache/spark/pull/482#discussion_r12131155
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -87,6 +88,75 @@ object ColumnPruning extends Rule[LogicalPlan] {
/**
* Replaces [[catalyst.expressions.Expression Expressions]] that can be
statically evaluated with
+ * equivalent [[catalyst.expressions.Literal Literal]] values. This rule
is more specific with
+ * Null value propagation from bottom to top of the expression tree.
+ */
+object NullPropagation extends Rule[LogicalPlan] {
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case q: LogicalPlan => q transformExpressionsUp {
+ // Skip redundant folding of literals.
+ case l: Literal => l
+ case e @ Count(Literal(null, _)) => Literal(0, e.dataType)
+ case e @ Sum(Literal(c, _)) if(c == 0) => Literal(0, e.dataType)
--- End diff --
Not like the previous implementation, I didn't add the null value as Child
expression for both Sum and Average in the rule, cause Hive will throw semantic
exception.
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