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https://issues.apache.org/jira/browse/CALCITE-1953?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16131306#comment-16131306
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MinJi Kim commented on CALCITE-1953:
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Here is my initial PR. Thanks!
https://github.com/apache/calcite/pull/521
> Reducing NOT() should not collaose NOT(IS_TRUE) to IS_FALSE for nullable
> inputs
> -------------------------------------------------------------------------------
>
> Key: CALCITE-1953
> URL: https://issues.apache.org/jira/browse/CALCITE-1953
> Project: Calcite
> Issue Type: Bug
> Reporter: MinJi Kim
> Assignee: Julian Hyde
>
> In RexSimplify, when simplifying NOT(), we negate the input expression. But
> for IS_FALSE/IS_TRUE/IS_NOT_FALSE/IS_NOT_TRUE this cannot be just negated if
> the input is nullable.
> {code}
> IS_FALSE(null) = false
> IS_TRUE(null) = false
> NOT(IS_FALSE(null)) = true != IS_TRUE(null)
> IS_NOT_FALSE(null) = true
> IS_NOT_TRUE(null) = true
> NOT(IS_NOT_FALSE(null)) = false != IS_NOT_TRUE(null)
> {code}
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