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https://issues.apache.org/jira/browse/PHOENIX-3005?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15338081#comment-15338081
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Lars Hofhansl commented on PHOENIX-3005:
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It's as simple as {{SELECT COUNT(DISTINCT c1) FROM T}} where there is an index
on c1. {{CREATE INDEX T_idx ON T(c1)}}. C1 is of type INTEGER.
In the debugger I see that the expression c1 (which we add to the GROUP BY
expression after removing the COUNT(DISTINCT) part) is not considered order
preserving.
> Use DistinctPrefixFilter for DISTINCT index scans
> -------------------------------------------------
>
> Key: PHOENIX-3005
> URL: https://issues.apache.org/jira/browse/PHOENIX-3005
> Project: Phoenix
> Issue Type: Sub-task
> Reporter: Lars Hofhansl
> Fix For: 4.8.0
>
>
> Currently the optimization in PHOENIX-258 is not used for DISTINCT index
> scans. We should add that as well.
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