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https://issues.apache.org/jira/browse/CALCITE-7722?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18105335#comment-18105335
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Julian Hyde commented on CALCITE-7722:
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Do you claim that it is valid to push {{IS NULL}} into an unsafe call? If so, I
disagree. It's not valid to convert "(1 / x) IS NULL" to "x IS NULL" because if
x is zero then the first expression will throw and the second will not.
> RexSimplify IS [NOT] NULL over a Strong.ANY call is no longer simplified when
> the call itself is unsafe
> -------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-7722
> URL: https://issues.apache.org/jira/browse/CALCITE-7722
> Project: Calcite
> Issue Type: Improvement
> Reporter: Thomas Rebele
> Assignee: Ruben Q L
> Priority: Major
> Labels: pull-request-available
>
> RexSimplify.simplifyIsNotNull / simplifyIsNull currently bail out of the
> whole simplification when the input RexCall is not fully safe (i.e.
> isSafeExpression(a) == false). This is stricter than necessary for operators
> with Strong.Policy.ANY, where IS [NOT] NULL(f(a, b, ...)) is semantically
> equivalent to IS [NOT] NULL(a) OR/AND IS [NOT] NULL(b) OR/AND ... — the
> operator itself does not need to be evaluated to compute the result.
> Example (regression for downstream projects such as Hive):
> {code}
> Before (≤ 1.34):
> IS NOT NULL(CAST(key AS DOUBLE) + 1.0) → IS NOT NULL(CAST(key AS DOUBLE))
> After (≥ 1.35):
> IS NOT NULL(CAST(key AS DOUBLE) + 1.0) → (unchanged)
> {code}
> The rewrite is dropped because CAST(key AS DOUBLE) + 1.0 is a non-lossless
> cast wrapped in a +, so isSafeExpression returns false, even though + is
> Strong.ANY and the distribution is a valid rewrite regardless of the outer
> call's safety.
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