Github user dilipbiswal commented on a diff in the pull request: https://github.com/apache/spark/pull/17330#discussion_r106884365 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/subquery.scala --- @@ -61,6 +63,37 @@ abstract class SubqueryExpression( } } +/** + * This expression is used to represent any form of subquery expression namely + * ListQuery, Exists and ScalarSubquery. This is only used to make sure the + * expression equality works properly when LogicalPlan.sameResult is called + * on plans containing SubqueryExpression(s). This is only a transient expression + * that only lives in the scope of sameResult function call. In other words, analyzer, + * optimizer or planner never sees this expression type during transformation of + * plans. + */ +case class CanonicalizedSubqueryExpr(expr: SubqueryExpression) + extends UnaryExpression with Unevaluable { + override def dataType: DataType = expr.dataType + override def nullable: Boolean = expr.nullable + override def child: Expression = expr + override def toString: String = s"CanonicalizedSubqueryExpr(${expr.toString})" + + // Hashcode is generated conservatively for now i.e it does not include the + // sub query plan. Doing so causes issue when we canonicalize expressions to + // re-order them based on hashcode. + // TODO : improve the hashcode generation by considering the plan info. + override def hashCode(): Int = { + val h = Objects.hashCode(expr.children) --- End diff -- @cloud-fan In my understanding, its because a SubqueryExpression contains a LogicalPlan and the logical plan has all sorts of expression ids that attributes to this unpredictability. In order to remove this, we may have to implement a canonicalize() on SubqueryExpression that also canonicalizes all the expressions on the subquery plan in a recursive fashion. I had marked it as a TODO in my comment. Please let me know if my understanding is wrong.
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