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https://issues.apache.org/jira/browse/CALCITE-7116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18011311#comment-18011311
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Julian Hyde commented on CALCITE-7116:
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I can't think of many cases where UNION ALL is more efficient than GROUPING
SETS but I have no objection to the rule. It is a valid transformation.
What is the name of the proposed class?
> Optimize queries with GROUPING SETS by converting them into equivalent UNION
> ALL of GROUP BY operations.
> --------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-7116
> URL: https://issues.apache.org/jira/browse/CALCITE-7116
> Project: Calcite
> Issue Type: New Feature
> Components: core
> Reporter: Zhen Chen
> Assignee: Yu Xu
> Priority: Minor
> Fix For: 1.41.0
>
>
> Currently, GROUPING SETS operations may not be optimally executed in some
> cases. This ticket proposes a rule to transform GROUPING SETS into a series
> of UNION ALL operations, each with its own GROUP BY clause.
> Original query:
> {code:java}
> SELECT a, b, c FROM t GROUP BY GROUPING SETS ((a,b), (a,c))
> {code}
> Transformed to:
> {code:java}
> SELECT a, b, NULL AS c FROM t GROUP BY a, b
> UNION ALL
> SELECT a, NULL AS b, c FROM t GROUP BY a, c
> {code}
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