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Posted to issues@calcite.apache.org by "Julian Hyde (JIRA)" <ji...@apache.org> on 2015/05/15 22:14:00 UTC

[jira] [Created] (CALCITE-732) Implement multiple distinct-COUNT using GROUPING SETS

Julian Hyde created CALCITE-732:
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             Summary: Implement multiple distinct-COUNT using GROUPING SETS
                 Key: CALCITE-732
                 URL: https://issues.apache.org/jira/browse/CALCITE-732
             Project: Calcite
          Issue Type: Bug
            Reporter: Julian Hyde
            Assignee: Julian Hyde


Currently if a query has COUNT(DISTINCT x) and COUNT(DISTINCT y) we compute the distinct counts separately and combine them using a join. The join isn't too expensive (because usually the GROUP BY has only a few keys) but we make multiple scans over the base table.

I think we could translate multiple distinct-counts into a GROUPING SETS query (i.e. an Aggregate with more than one element in the groupSets field). If the underlying engine can evaluate that efficiently, then we have saved ourselves a join and several scans.



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