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https://issues.apache.org/jira/browse/CALCITE-4511?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17288857#comment-17288857
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Liya Fan edited comment on CALCITE-4511 at 2/23/21, 5:50 AM:
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[~julianhyde] Thanks for your feedback.
{{NDV(i, j)}} means
{noformat}
NDV ({i, j})
{noformat}
That is, the number of distinct values for columns {{i}} and {{j}}.
(i and j are column indices)
In the Calcite code, it should correspond to
{{RelMetadataQuery#getDistinctRowCount(ImmutableBitSet.of(i, j))}}
was (Author: fan_li_ya):
[~julianhyde] Thanks for your feedback.
{{NDV(i, j)}} means
{noformat}
NDV ({i, j})
{noformat}
That is, the number of distinct values for columns {{i}} and {{j}}.
In the Calcite code, it should correspond to
{{RelMetadataQuery#getDistinctRowCount(ImmutableBitSet.of(i, j))}}
> 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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