Github user dilipbiswal commented on a diff in the pull request:
https://github.com/apache/spark/pull/17541#discussion_r110212520
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/QueryPlan.scala
---
@@ -359,9 +359,47 @@ abstract class QueryPlan[PlanType <:
QueryPlan[PlanType]] extends TreeNode[PlanT
override protected def innerChildren: Seq[QueryPlan[_]] = subqueries
/**
- * Canonicalized copy of this query plan.
+ * Returns a plan where a best effort attempt has been made to transform
`this` in a way
+ * that preserves the result but removes cosmetic variations (case
sensitivity, ordering for
+ * commutative operations, expression id, etc.)
+ *
+ * Plans where `this.canonicalized == other.canonicalized` will always
evaluate to the same
+ * result.
+ *
+ * Some leaf nodes should overwrite this to provide proper canonicalize
logic.
*/
- protected lazy val canonicalized: PlanType = this
+ lazy val canonicalized: PlanType = {
+ val canonicalizedChildren = children.map(_.canonicalized)
+ withNewChildren(canonicalizedChildren) mapExpressions {
+ case a: Alias =>
+ // As the root of the expression, Alias will always take an
arbitrary exprId, we need to
+ // erase that for equality testing. The alias name doesn't matter
and should also be erased.
+ Alias(normalizeExprId(a.child), "")(ExprId(-1), a.qualifier,
isGenerated = a.isGenerated)
+
+ case ar: AttributeReference if allAttributes.indexOf(ar.exprId) ==
-1 =>
+ // Top level `AttributeReference` may also be used for output like
`Alias`, we should
+ // erase the epxrId too.
+ ar.withExprId(ExprId(-1))
+
+ case other => normalizeExprId(other)
+ }
+ }
+
+ /**
+ * Normalize the exprIds in the given expression, by updating the exprId
in `AttributeReference`
+ * with its referenced ordinal from input attributes. It's similar to
`BindReferences` but we
+ * do not use `BindReferences` here as the plan may take the expression
as a parameter with type
+ * `Attribute`, and replace it with `BoundReference` will cause error.
+ */
+ private def normalizeExprId(e: Expression): Expression = e.canonicalized
transformUp {
+ case ar: AttributeReference =>
+ val ordinal = allAttributes.indexOf(ar.exprId)
+ if (ordinal == -1) {
+ ar
+ } else {
+ ar.withExprId(ExprId(ordinal))
--- End diff --
@cloud-fan this is very nice idea :-) I was running into the same issue
when you asked me to try normalizing the attributes in my caching pr.
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