[GitHub] [spark] cloud-fan commented on a change in pull request #29585: [SPARK-32741][SQL] Check if the same ExprId refers to the unique attribute in logical plans

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cloud-fan commented on a change in pull request #29585:
URL: https://github.com/apache/spark/pull/29585#discussion_r483444401



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
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@@ -203,3 +203,57 @@ abstract class BinaryNode extends LogicalPlan {
 abstract class OrderPreservingUnaryNode extends UnaryNode {
   override final def outputOrdering: Seq[SortOrder] = child.outputOrdering
 }
+
+object LogicalPlanIntegrity {
+
+  private def canGetOutputAttrs(p: LogicalPlan): Boolean = {
+    p.resolved && !p.expressions.exists { e =>
+      e.collectFirst {
+        // We cannot call `output` in plans with a `ScalarSubquery` expr having no column,
+        // so, we filter out them in advance.
+        case s: ScalarSubquery if s.plan.schema.fields.isEmpty => true
+      }.isDefined
+    }
+  }
+
+  /**
+   * Since some logical plans (e.g., `Union`) can build `AttributeReference`s in their `output`,
+   * this method checks if the same `ExprId` refers to a semantically-equal attribute
+   * in a plan output.
+   */
+  def hasUniqueExprIdsForOutput(plan: LogicalPlan): Boolean = {
+    val allOutputAttrs = plan.collect { case p if canGetOutputAttrs(p) =>
+      p.output.filter(_.resolved).map(_.canonicalized.asInstanceOf[Attribute])
+    }
+    val groupedAttrsByExprId = allOutputAttrs
+      .flatten.groupBy(_.exprId).values.map(_.distinct)
+    groupedAttrsByExprId.forall(_.length == 1)
+  }
+
+  /**
+   * This method checks if reference `ExprId`s are not reused when assigning a new `ExprId`.
+   * For example, it returns false if plan transformers create an alias having the same `ExprId`
+   * with one of reference attributes, e.g., `a#1 + 1 AS a#1`.
+   */
+  def checkIfSameExprIdNotReused(plan: LogicalPlan): Boolean = {
+    plan.map { p =>
+      p.expressions.filter(_.resolved).forall { e =>
+        val namedExprs = e.collect {
+          case ne: NamedExpression if !ne.isInstanceOf[LeafExpression] => ne

Review comment:
       I think we can do a simple check: find all the `Alias` in this plan, and check the expr ID of `Alias` doesn't exist in the `inputSet`.




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