[SPARK-38832][SQL][FOLLOWUP] Support propagate empty expression set for distinct key #36281
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cloud-fan
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Apr 20, 2022
...catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/DistinctKeyVisitor.scala
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cloud-fan
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Apr 20, 2022
...catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/DistinctKeyVisitor.scala
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cloud-fan
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wangyum
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Apr 21, 2022
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@wangyum what's wrong with that code? |
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For example: Set[ExpressionSet](ExpressionSet()).exists(_.subsetOf(ExpressionSet(ae.aggregateFunction.children.filterNot(_.foldable))))It is always true, it may have potential problems. |
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if we get an unexpected empty ExpressionSet it should be a bug .. shall we trust the framework ? |
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I don't see why empty expression set is special. If the framework has bugs and produces incorrect distinct keys, we will have query correctness bugs. |
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I'm ok if you do not think it is needed. |
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My point is empty expression set is informative and we shouldn't skip it. It means the data is distinct by Nil, so it has at most 1 row and can override any other distinct keys. |
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thanks, merging to master! |
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thank you @wangyum @cloud-fan |
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What changes were proposed in this pull request?
DistinctKeyVisitorthat support propagate empty setWhy are the changes needed?
Make distinct keys can be used to optimize more case, see comment #36117 (comment)
Does this PR introduce any user-facing change?
Improve performance
How was this patch tested?
add test