Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/17330#discussion_r107331403
--- 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)
--- End diff --
Do we really need this new abstraction?
Actually I don't think we should compare `SubqueryExpression`s and wonder
how to canonicalize them.
Basically, in `sameResult`, by adding new condition `(left.subqueries,
right.subqueries).zipped.forall(_ sameResult _)`, we can achieve the same goal
and all added tests are passed.
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