Ruben Q L created CALCITE-4623:
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Summary: Review if SemiJoinRule shall / shall not match SEMI join
Key: CALCITE-4623
URL: https://issues.apache.org/jira/browse/CALCITE-4623
Project: Calcite
Issue Type: Task
Components: core
Affects Versions: 1.26.0
Reporter: Ruben Q L
Issue pointed out by [~zabetak] during the review of CALCITE-4621.
Currently, SemiJoinRule (both {{CoreRules.JOIN_TO_SEMI_JOIN}} and
{{CoreRules.PROJECT_TO_SEMI_JOIN}}) matches INNER, LEFT and SEMI join. This
last join type seems a bit bizarre (why matching a SEMI join if the purpose of
this rule is precisely generating one).
It seems that SEMI was introduced in the rule by the "big join design
refactoring" (see CALCITE-2969 and
[4809393|https://github.com/apache/calcite/commit/48093937ae4db179884d1111fa9d12e978e57e1f]).
The purpose of this ticket is to confirm whether or not processing SEMI in
SemiJoinRule makes sense (and if not, remove it).
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