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https://issues.apache.org/jira/browse/CALCITE-695?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14521990#comment-14521990
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Sean Hsuan-Yi Chu commented on CALCITE-695:
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Sent a pull request:
https://github.com/apache/incubator-calcite/pull/80
Util.java has a new method to determine if the output for a subquery is scalar.
Essentially, when this method suggests scalar output, no necessity to add
SqlSingleValueAggFunction.
> SqlSingleValueAggFunction is created when it may not be needed
> --------------------------------------------------------------
>
> Key: CALCITE-695
> URL: https://issues.apache.org/jira/browse/CALCITE-695
> Project: Calcite
> Issue Type: Bug
> Affects Versions: 1.3.0-incubating
> Reporter: Aman Sinha
> Assignee: Julian Hyde
>
> In the following query, the subquery is producing a scalar value but the
> logical plan still creates a SqlSingleValueAggFunction.
> {code}
> select r_regionkey from region
> where r_regionkey > (select min(n_regionkey) * 2 from nation);
> {code}
> If the aggregate is just min(n_regionkey) instead of the expression
> min(n_regionkey) * 2 then no SqlSingleValueAggFunction is created. Ideally,
> both should behave the same.
> This is not necessarily a bug but it does create a burden on the underlying
> execution engine to support this function even in cases where it may not be
> needed.
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