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https://issues.apache.org/jira/browse/PHOENIX-2989?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15326466#comment-15326466
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Lars Hofhansl commented on PHOENIX-2989:
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That seems easy enough to do. Are you sure that is no way to combine these
COUNT(DISTINCT) expressions in ways that prevent the optimization from working
correctly?
> Allow DistinctPrefixFilter optimization when HAVING or ORDER BY clauses only
> reference COUNT(DISTINCT)
> ------------------------------------------------------------------------------------------------------
>
> Key: PHOENIX-2989
> URL: https://issues.apache.org/jira/browse/PHOENIX-2989
> Project: Phoenix
> Issue Type: Sub-task
> Reporter: James Taylor
> Fix For: 4.8.0
>
>
> The DistinctPrefixFilter optimization can still be used if a HAVING or ORDER
> BY clause only references COUNT(DISTINCT) expressions. One way to detect this
> is to collect a Set<ParseNode> using a visitor for the SELECT, HAVING, and
> ORDER BY which only collects COUNT(DISTINCT) expressions. This set will then
> be used as the GROUP BY nodes if there's no existing GROUP BY.
> The check for whether or not to add the filter can then change to something
> like this:
> {code}
> if (... &&
> plan.getGroupBy().isUngroupedAggregate() &&
> plan.getGroupBy().getKeyExpressions().size() ==
> context.getAggregationManager().getAggregators().getAggregatorCount() )
> {code}
> That way, it'll only add the filter if all expressions pulled in as a GROUP
> BY expression (only the count distinct ones) account for all of the
> aggregators.
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