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https://issues.apache.org/jira/browse/CALCITE-2973?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16813853#comment-16813853
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Julian Hyde commented on CALCITE-2973:
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[~hyuan], I mostly agree. For the record, here is a non-equi join where you can
use a hash join plus a per-row condition, where the 'equi' part of the
condition is fairly selective and therefore hash join makes sense. It has to be
done as a per-row condition, rather than a filter after the join, because of
the {{left outer}}.
{code:java}
select *
from emp left join dept
on emp.deptno = dept.deptno
and emp.age < 30{code}
> Allow theta joins that have equi conditions to be executed using a merge join
> or hash join algorithm
> ----------------------------------------------------------------------------------------------------
>
> Key: CALCITE-2973
> URL: https://issues.apache.org/jira/browse/CALCITE-2973
> Project: Calcite
> Issue Type: New Feature
> Components: core
> Affects Versions: 1.19.0
> Reporter: Lai Zhou
> Priority: Minor
>
> Now the EnumerableMergeJoinRule only supports an inner and equi join.
> If users make a theta-join query for a large dataset (such as 10000*10000),
> the nested-loop join process will take dozens of time than the sort-merge
> join process .
> So if we can apply merge-join or hash-join rule for a theta join, it will
> improve the performance greatly.
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