[jira] [Commented] (CALCITE-7242) Implement a rule to eliminate LITERAL_AGG so that other databases can handle it

["weihua zhang (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-7242?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18032701#comment-18032701 ] 

weihua zhang commented on CALCITE-7242:
---------------------------------------

[~scarlin] can you help review this [PR|https://github.com/apache/calcite/pull/4598]? My commit is adapted from your implementation.

> Implement a rule to eliminate LITERAL_AGG so that other databases can handle it
> -------------------------------------------------------------------------------
>
>                 Key: CALCITE-7242
>                 URL: https://issues.apache.org/jira/browse/CALCITE-7242
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>            Reporter: weihua zhang
>            Priority: Major
>              Labels: pull-request-available
>
> Calcite can create an Aggregate RelNode with LITERAL_AGG AggregateCall to check for existence in a subquery. In this case, the Aggregate will do a group by, and just spit out a literal value for each row.
> The LITERAL_AGG function does not exist in other databases. In order to create a RelNode structure that other databases supports, this Aggregate is turned into an Aggregate that still does the "group by" on the relevant groups, but places a Project RelNode on top that returns the literal value.



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