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https://issues.apache.org/jira/browse/FLINK-15979?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Konstantin Knauf reopened FLINK-15979:
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Re-opening in accordance with https://issues.apache.org/jira/browse/FLINK-23206.
> Fix the merged count is not accurate in CountDistinctWithMerge
> ---------------------------------------------------------------
>
> Key: FLINK-15979
> URL: https://issues.apache.org/jira/browse/FLINK-15979
> Project: Flink
> Issue Type: New Feature
> Components: Table SQL / Legacy Planner
> Reporter: Jark Wu
> Priority: Minor
> Labels: auto-closed
>
> As discussed in the user ML:
> https://lists.apache.org/thread.html/rc4b06c9931656c94dc993b124da3ff00f04099e41201c64788936c24%40%3Cuser.flink.apache.org%3E.
> The current implementation of
> {{org.apache.flink.table.runtime.utils.JavaUserDefinedAggFunctions.CountDistinctWithMerge#merge}}
> in old planner is not correct which will have a wrong merged count.
> The test
> (org.apache.flink.table.runtime.stream.table.GroupWindowITCase#testEventTimeSessionGroupWindowOverTime)
> which uses this UDAF can't expose the bug because there are no distinct
> values in the test data.
> The class {{CountDistinctWithMerge}} is a testing implementation which is not
> a critical problem. Blink planner has a correct implementation:
> https://github.com/apache/flink/blob/master/flink-table/flink-table-planner-blink/src/test/java/org/apache/flink/table/planner/plan/utils/JavaUserDefinedAggFunctions.java#L369
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