Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/10844#discussion_r51068802
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/QueryPlan.scala
---
@@ -17,16 +17,31 @@
package org.apache.spark.sql.catalyst.plans
-import org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeSet,
Expression, VirtualColumn}
+import org.apache.spark.sql.catalyst.expressions._
import org.apache.spark.sql.catalyst.trees.TreeNode
import org.apache.spark.sql.types.{DataType, StructType}
-abstract class QueryPlan[PlanType <: TreeNode[PlanType]] extends
TreeNode[PlanType] {
+abstract class QueryPlan[PlanType <: TreeNode[PlanType]]
+ extends TreeNode[PlanType] with PredicateHelper {
self: PlanType =>
def output: Seq[Attribute]
/**
+ * Extracts the output property from a given child.
+ */
+ def extractConstraintsFromChild(child: QueryPlan[PlanType]):
Set[Expression] = {
+ child.constraints.filter(_.references.subsetOf(outputSet))
+ }
+
+ /**
+ * An sequence of expressions that describes the data property of the
output rows of this
+ * operator. For example, if the output of this operator is column `a`,
an example `constraints`
+ * can be `Set(a > 10, a < 20)`.
+ */
+ def constraints: Set[Expression] = Set.empty
--- End diff --
This is probably going to be nontrivial to calculate for a large tree. We
might consider having an internal method, `private def validConstraints` or
something, that we expand / canonicalize into a `lazy val constraints`
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