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https://issues.apache.org/jira/browse/CALCITE-5117?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17529158#comment-17529158
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xiong duan commented on CALCITE-5117:
-------------------------------------
Fixed in
[3db4dd1|https://github.com/apache/calcite/commit/3db4dd1ebf04abaf74d29464ae311a598ae929f7].
Thanks for the review [~Chunwei Lei] .
> Optimize the EXISTS sub-query by Metadata RowCount
> --------------------------------------------------
>
> Key: CALCITE-5117
> URL: https://issues.apache.org/jira/browse/CALCITE-5117
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.30.0
> Reporter: xiong duan
> Assignee: xiong duan
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.31.0
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> As same as the UNIQUE sub-query, before we convert the sub-query to RelNode.
> we use the Metadata to optimize it.
> EXISTS sub-query, If the sub-query is guaranteed to produce at least one row,
> just return TRUE. If the sub-query is guaranteed to produce no row, just
> return FALSE.
> For example:
> {code:java}
> select *
> from dept as d
> where EXISTS (select count(*) from emp e where d.deptno = e.deptno){code}
> We can optimize it to:
> {code:java}
> EnumerableTableScan(table=[[scott, DEPT]]){code}
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