Github user hvanhovell commented on a diff in the pull request:
https://github.com/apache/spark/pull/17993#discussion_r116793889
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
---
@@ -54,6 +54,59 @@ object ConstantFolding extends Rule[LogicalPlan] {
}
}
+/**
+ * Substitutes [[Attribute Attributes]] which can be statically evaluated
with their corresponding
+ * value in conjunctive [[Expression Expressions]]
+ * eg.
+ * {{{
+ * SELECT * FROM table WHERE i = 5 AND j = i + 3
+ * ==> SELECT * FROM table WHERE i = 5 AND j = 8
+ * }}}
+ */
+object ConstantPropagation extends Rule[LogicalPlan] with PredicateHelper {
+
+ def containsNonConjunctionPredicates(expression: Expression): Boolean =
expression match {
+ case Not(_) => true
+ case Or(_, _) => true
+ case _ =>
+ var result = false
+ expression.children.foreach {
+ case Not(_) => result = true
+ case Or(_, _) => result = true
+ case other => result = result ||
containsNonConjunctionPredicates(other)
+ }
+ result
+ }
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case q: LogicalPlan => q transformExpressionsUp {
+ case and @ (left And right)
+ if !containsNonConjunctionPredicates(left) &&
!containsNonConjunctionPredicates(right) =>
+
+ val leftEntries = left.collect {
+ case e @ EqualTo(left: AttributeReference, right: Literal) =>
((left, right), e)
+ case e @ EqualTo(left: Literal, right: AttributeReference) =>
((right, left), e)
+ }
+ val rightEntries = right.collect {
+ case e @ EqualTo(left: AttributeReference, right: Literal) =>
((left, right), e)
+ case e @ EqualTo(left: Literal, right: AttributeReference) =>
((right, left), e)
+ }
+ val constantsMap = AttributeMap(leftEntries.map(_._1) ++
rightEntries.map(_._1))
+ val predicates = (leftEntries.map(_._2) ++
rightEntries.map(_._2)).toSet
+
+ def replaceConstants(expression: Expression) = expression
transform {
+ case a: AttributeReference if constantsMap.contains(a) =>
--- End diff --
What happens if I do something stupid like `i = 1 and ((j = 1) = (j = i))`?
I think `j = 1` might replaced by `1 = 1`.
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