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https://issues.apache.org/jira/browse/CALCITE-7479?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18074667#comment-18074667
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Zhen Chen commented on CALCITE-7479:
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Although I’ve submitted a PR, it’s currently just a draft. I’d like to hear if
anyone has any other suggestions regarding this Jira issue.
> Remove redundant aggregate group keys with FD
> ---------------------------------------------
>
> Key: CALCITE-7479
> URL: https://issues.apache.org/jira/browse/CALCITE-7479
> Project: Calcite
> Issue Type: New Feature
> Components: core
> Affects Versions: 1.41.0
> Reporter: Zhen Chen
> Priority: Minor
> Labels: pull-request-available
>
> {*}Proposal{*}
> Add a new {{AGGREGATE}} rewrite rule to identify and remove redundant
> grouping keys from an {{AGGREGATE}} that are functionally determined by
> preceding grouping keys. To preserve the original semantics, the rewrite will:
> * Shorten the grouping key list of the {{AGGREGATE}}
> * Use SINGLE_VALUE to restore the removed grouping column(s)
> * Reorder the output columns to match the original order using a {{PROJECT}}
> {*}Example of the Planned Change{*}
> Original SQL:
> {code:java}
> select deptno, name, count() as c
> from sales.dept
> group by deptno, name {code}
> Original plan:
> {code:java}
> LogicalAggregate(group=[{0, 1}], C=[COUNT()])
> LogicalTableScan(table=[[CATALOG, SALES, DEPT]]) {code}
> Rewritten plan:
> {code:java}
> LogicalProject(DEPTNO=[$0], NAME=[$1], C=[$2])
> LogicalAggregate(group=[{0}], NAME=[SINGLE_VALUE($1)], C=[COUNT()])
> LogicalTableScan(table=[[CATALOG, SALES, DEPT]]) {code}
> {*}Explanation{*}
> If {{{}name{}}}is functionally determined by {{{}deptno{}}}, then
> {{{}name{}}}is removed from the grouping keys.
> * SINGLE_VALUE is used to retain the value of the removed column
> semantically.
> * The PROJECT restores the final output column order and field names.
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