viirya commented on a change in pull request #25204: [SPARK-28441][SQL][Python]
Fix error when non-foldable expression is used in correlated scalar subquery
URL: https://github.com/apache/spark/pull/25204#discussion_r307223851
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -650,7 +650,9 @@ object ColumnPruning extends Rule[LogicalPlan] {
*/
private def removeProjectBeforeFilter(plan: LogicalPlan): LogicalPlan = plan
transformUp {
case p1 @ Project(_, f @ Filter(_, p2 @ Project(_, child)))
- if p2.outputSet.subsetOf(child.outputSet) =>
+ if p2.outputSet.subsetOf(child.outputSet) &&
+ // We only remove attribute-only project.
+ p2.projectList.forall(_.isInstanceOf[AttributeReference]) =>
Review comment:
oh, the issue was seen in previous comment
https://github.com/apache/spark/pull/25204/commits/33441a32412eacbe84f2b188f046b2959a8b60ee.
It was overwritten now.
We added a column for count bug. The column checks a always-true leading
column `alwaysTrueExpr`, returns special value if `alwaysTrueExpr` is null, to
simulate empty input case.
This column reuses expr id of original output in the subquery. In
non-foldable expression case, the added column in a potential
Project-Filter-Project, will be trimmed by `removeProjectBeforeFilter`, because
the second project meets `p2.outputSet.subsetOf(child.outputSet)`.
My original fix is to create an expr id. Replace original expr id with new
one in the subquery. Looks complicated. This seems a simple fix, and looks
reasonable.
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