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https://issues.apache.org/jira/browse/CALCITE-1526?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15722119#comment-15722119
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Jesus Camacho Rodriguez commented on CALCITE-1526:
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{{RexUtil.ExprSimplifier}} traverses the expression and simplifies it, choosing
whether to recognize UNKNOWN as FALSE depending on 1) the initial value for _
unknownAsFalseCall_, and 2) the expressions found in the traversal.
[~julianhyde], I think it could be extended to use Strong indeed, by checking
whether a subexpression might produce UNKNOWN and choosing accordingly the
simplify method to call in RexUtil. However, I am still doubting whether that
would help to detect further simplification opportunities, or it would just
help simplifying/unifying the different code paths.
> Use Strong to infer whether a predicate's inputs may be null
> ------------------------------------------------------------
>
> Key: CALCITE-1526
> URL: https://issues.apache.org/jira/browse/CALCITE-1526
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Julian Hyde
>
> {{RexImplicationChecker}} must use
> [Strong|https://calcite.apache.org/apidocs/org/apache/calcite/plan/Strong.html]
> to infer whether a predicate's inputs may be null. In particular the code in
> {{RexImplicationChecker.implies2}}.
> Also {{RelMdPredicates.projectPredicate}}.
> [~jcamachorodriguez], Could/should {{RexUtil.ExprSimplifier}} be using
> {{Strong}}?
> Also, maybe, {{RexUtil.simplifyIs}}.
> Also, {{LogicVisitor}} might be able to deduce that an expression is never
> null if certain input fields are not null.
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