[jira] [Commented] (CALCITE-4511) The number of distinct values for constant columns should be 1

["Julian Hyde (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-4511?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17288842#comment-17288842 ] 

Julian Hyde commented on CALCITE-4511:
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NDV is not a Calcite concept. Can you please explain NDV(i) and NDV(i, j) in Calcite terms?

> The number of distinct values for constant columns should be 1
> --------------------------------------------------------------
>
>                 Key: CALCITE-4511
>                 URL: https://issues.apache.org/jira/browse/CALCITE-4511
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>            Reporter: Liya Fan
>            Assignee: Liya Fan
>            Priority: Major
>
> Suppose we have a relation with 3 columns: {{(a, '1', '2')}}. The first column comes from an underlying table, while the other two columns are constants. 
> For this relation, we should have {{NDV(1) = 1}}, since column 1 is a constant, which have only one possible value (suppose the column index starts from 0).
> Similarly, we should have {{NDV(1, 2) = 1}}, since both columns are constants.
> We should also have {{NDV(0, 1) == NDV(0)}}, because the number of distinct values depends on the non-const column, which is {{a}} from the underlying table. 



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