Maryann Xue created CALCITE-1628:
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Summary: Add an alternative match pattern for SemiJoinRule
Key: CALCITE-1628
URL: https://issues.apache.org/jira/browse/CALCITE-1628
Project: Calcite
Issue Type: Improvement
Components: core
Affects Versions: 1.11.0
Reporter: Maryann Xue
Assignee: Maryann Xue
Priority: Minor
Fix For: 1.12.0
SemiJoinRule looks for an INNER or LEFT OUTER Join with its right child as an
Aggregate. It also tries to match a Project as the parent of the Join so that
it can abort if any columns from the right child of the Join is referenced.
There is another situation though, where the right child is an empty Aggregate
that returns 0 columns and thus we don't need to look for a Project. So an
alternative match pattern for SemiJoinRule would be just a Join over an
Aggregate without a Project. For example, the following query can match the
alternative pattern and fire the rule:
{code}
select e."deptno" from "hr"."emps" as e left join (select count(*) from
"hr"."depts") on true
{code}
, where after field trimming the inner query will become an empty Aggregate.
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