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https://issues.apache.org/jira/browse/CALCITE-5294?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17608431#comment-17608431
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Julian Hyde commented on CALCITE-5294:
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[~kkasa], I reviewed your changes, and they look good. In my
[julianhyde/5294-prune-join|https://github.com/julianhyde/calcite/tree/5294-prune-join]
branch I added a further commit that makes the logic more concise. Please let
me know what you think of my changes. If you approve I will squash and merge to
main.
> Improve PruneEmptyRules join instances to remove join if generates null and
> one branch is empty
> -----------------------------------------------------------------------------------------------
>
> Key: CALCITE-5294
> URL: https://issues.apache.org/jira/browse/CALCITE-5294
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Krisztian Kasa
> Assignee: Krisztian Kasa
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.33.0
>
> Time Spent: 3.5h
> Remaining Estimate: 0h
>
> If a {{Join}} generates null on the right and the right branch of the join
> known never produces any rows the join can be replaced with the left branch
> and a project on top of it which contains the expressions come from the left
> branch and null constants from the right branch. Example:
> {code:java}
> select * from emp e
> left outer join (select * from dept where false) as d on e.deptno = d.deptno
> {code}
> {code:java}
> select
> e.*,
> cast(null as <dept_col0_type>) as <dept_col0_name>
> ...
> cast(null as <dept_coln_type>) as <dept_coln_name>
> from emp
> {code}
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