[
https://issues.apache.org/jira/browse/CALCITE-2421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16770930#comment-16770930
]
Zoltan Haindrich commented on CALCITE-2421:
-------------------------------------------
this right now is only working for {{UnknownAs.FALSE}} - and only when the type
is not nullable. [link to
code|https://github.com/apache/calcite/blob/ef9f926061de21ad713a76ec3ec8110e5cbd92bf/core/src/main/java/org/apache/calcite/rex/RexSimplify.java#L306]
we could instead of that could generally rewrite
* {{A=A}} to {{A IS NOT NULL OR NULL}} (similarily <=,>=)
* {{A!=A}} to {{A IS NULL AND NULL}} (similarily <,>)
With these and the existing unknownAs logics ; this could became true/false A
IS [NOT] NULL correctly ; but when those cases does not apply it would at worst
retain the same number of RexNodes (I was afraid that it would raise it):
* {{w(A=A) = 2w(A) +1 }}
* {{w(A IS NOT NULL OR NULL)=w(A) + 2}}
* if we consider that {{w(A)>=1}} we are at worst at the same node count
> 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.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
