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https://issues.apache.org/jira/browse/CALCITE-5780?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17733270#comment-17733270
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Runkang He commented on CALCITE-5780:
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[~nobigo] `1 > x or x >=1 or x is null` is not handled in the past, and can be
simplified to TRUE in this Jira's commit.
An interesting thing is `x >=1 or 1 > x or x is null` can be simplified to TRUE
in the past, there are two points to explain why:
1. When simplify OR terms, we move `x is null` to term list's head, and then,
inverse each term one by one. When inverse `x >= 1`(i.e. `is not true(x >=
1)`), it can be simplified to `x < 1`, which can be used in further
simplification.
2. When simpify predicate with pulled up predicates, the `1 > x` is processed
and represented using Comparison, which can handle it properly.
Back to `1 > x or x >=1 or x is null`, the reason why it is not handled in the
past is basically the opposite:
1. When inverse `1 > x`(i.e. `is not true(1 > x)`), it cannot be simplified to
`1 <= x` because isEffectivelyNotNull logic for `1 > x` when pulled up
predicates contain `x is not null` is missing. So the simplified result is `is
not true(1 > x)`(not changed), but it can and should be {*}`1 <= x`{*}, and we
need it for further simplification.
2. After we conside reverse comparison case and improve the logic, when simpify
predicate `x >=1` with pulled up predicates(`x is not null`, {*}`1 <= x`{*}),
the `1 <= x` in pulled up predicates is not handled.
> Always-true OR expressions contain reverse order comparison should be
> simplified to TRUE
> ----------------------------------------------------------------------------------------
>
> Key: CALCITE-5780
> URL: https://issues.apache.org/jira/browse/CALCITE-5780
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.34.0
> Reporter: Runkang He
> Assignee: Runkang He
> Priority: Major
> Labels: pull-request-available
>
> The following expressions which contain reverse order comparison are always
> true:
> {code:sql}
> 1 > x or 1 <= x or x is null
> 1 < x or 1 >= x or x is null
> 1 > x or 0 < x or x is null
> {code}
> But currently these expressions are not fully simplified to TRUE, the current
> simplified results are SEARCH operator.
> The root cause is that RexSimplify doesn't identify these cases and makes
> targeted simplification.
> It would be nice if RexSimplify.simplifyOr handled these cases.
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