agubichev commented on code in PR #43111:
URL: https://github.com/apache/spark/pull/43111#discussion_r1345929714
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/DecorrelateInnerQuery.scala:
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@@ -461,6 +462,23 @@ object DecorrelateInnerQuery extends PredicateHelper {
p.mapChildren(rewriteDomainJoins(outerPlan, _, conditions))
}
+ private def isCountBugFree(aggregateExpressions: Seq[NamedExpression]):
Boolean = {
+ // The COUNT bug only appears if an aggregate expression returns a
non-NULL result on an empty
+ // input.
+ // Typical example (hence the name) is COUNT(*) that returns 0 from an
empty result.
+ // However, SUM(x) IS NULL is another case that returns 0, and in general
any IS/NOT IS and CASE
+ // expressions are suspect (and the combination of those).
+ // For now we conservatively accept only those expressions that are
guaranteed to be safe.
+ val exprsRejectEmptyInput = aggregateExpressions.map {
+ case _ : AttributeReference => true
+ case Alias(_: AttributeReference, _) => true
+ case Alias(_: Literal, _) => true
+ case Alias(a: AggregateExpression, _) if
a.aggregateFunction.defaultResult == None => true
+ case _ => false
+ }
+ exprsRejectEmptyInput.forall(x => x == true)
Review Comment:
neat, thank you!
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