[jira] [Commented] (CALCITE-1488) ValuesReduceRule should ignore empty Values

["Gian Merlino (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-1488?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15657351#comment-15657351 ] 

Gian Merlino commented on CALCITE-1488:
---------------------------------------

Thanks [~julianhyde]! I applied this patch locally and it works for me.

I still have a problem with Aggregates that lack a group set, like SELECT COUNT(*) FROM s.foo WHERE 1 = 0. PruneEmptyRules doesn't reduce that, since the result is going to be one row, not empty. The ValuesReduceRules don't either, because they don't touch Aggregates.

I ended up addressing this with a rule on my end: https://gist.github.com/gianm/1c192a47a7ce284be8af986f97e6dd8f

Does that approach make sense? If so do you think it makes sense to contribute to Calcite?

One thing I'm not sure about is if there's a better way to figure out what should be 0 and what should be NULL other than hard-coding COUNT and SUM0.

> ValuesReduceRule should ignore empty Values
> -------------------------------------------
>
>                 Key: CALCITE-1488
>                 URL: https://issues.apache.org/jira/browse/CALCITE-1488
>             Project: Calcite
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 1.10.0
>            Reporter: Gian Merlino
>            Assignee: Julian Hyde
>             Fix For: 1.11.0
>
>
> ValuesReduceRule doesn't propagate rowType on Project of empty Values. If ValuesReduceRule is trying to reduce a Project on top of an empty Values, then changeCount ends up 0, and it returns the underlying Values. This leads to an assertion failure because the returned Values does not have the expected rowType.
> One way to fix this is changing the "Filter had no effect" logic from "{{changeCount == 0}}" to "{{changeCount == 0 && projectExprs == null}}".



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