Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/482#discussion_r12036292
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -91,10 +91,53 @@ object ColumnPruning extends Rule[LogicalPlan] {
*/
object ConstantFolding extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = plan transform {
- case q: LogicalPlan => q transformExpressionsDown {
+ case q: LogicalPlan => q transformExpressionsUp {
// Skip redundant folding of literals.
case l: Literal => l
+ // if it's foldable
case e if e.foldable => Literal(e.eval(null), e.dataType)
+ case e @ Count(Literal(null, _)) => Literal(null, e.dataType)
+ case e @ Sum(Literal(null, _)) => Literal(null, e.dataType)
+ case e @ Average(Literal(null, _)) => Literal(null, e.dataType)
+ case e @ IsNull(Literal(null, _)) => Literal(true, BooleanType)
--- End diff --
Some of these already fold correctly.
```scala
scala> sql("SELECT null IS NULL")
res4: org.apache.spark.sql.SchemaRDD =
SchemaRDD[0] at RDD at SchemaRDD.scala:96
== Query Plan ==
Project [true AS c0#0]
```
Maybe we should write tests for each case, before adding the rule, to make
sure it is broken.
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