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https://issues.apache.org/jira/browse/CALCITE-2421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16549945#comment-16549945
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Laurent Goujon commented on CALCITE-2421:
-----------------------------------------
Here's a pull request: https://github.com/apache/calcite/pull/765
I removed the {{withUnknownAsFalse(false)}} from
{{RexSimplify#simplifyAndTerms()}} but I'm nervous I haven't found of some
condition where this would be necessary (and there has been no existing unit
tests failing because of that change).
> RexSimplify#simplifyAnds foregoes some simplications if unknownAsFalse set to
> true
> ----------------------------------------------------------------------------------
>
> Key: CALCITE-2421
> URL: https://issues.apache.org/jira/browse/CALCITE-2421
> Project: Calcite
> Issue Type: Bug
> Reporter: Laurent Goujon
> Assignee: Laurent Goujon
> Priority: Minor
>
> It looks like {{RexSimplify#simplifyAnds}} foregoes some comparison
> simplifications if {{unknownAsFalse}} is set to true, like {{A = A AND B =
> B}} which might be simplified to {{A IS NOT NULL AND B IS NOT NULL}} or even
> {{true}} if {{A}} and {{B}} are known to be not nullable.
> One consequence of this is that the selectivity value might be off as a {{=}}
> comparison has a selectivity of 15% whereas {{IS NOT NULL}} has a selectivity
> of 90%.
> The simplication is skipped because {{RexSimplify#simplifyList}} simplify all
> terms with {{unknownAsFalse}} set to {{false}}, but in
> {{RexSimplify#simplifyAnd2ForUnknownAsFalse}}, there's no attempt at trying
> again to simplify each term.
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