Uploaded image for project: 'Calcite'
  1. Calcite
  2. CALCITE-732

Implement multiple distinct-COUNT using GROUPING SETS

          Details

          • Type: Bug
          • Status: Closed
          • Priority: Major
          • Resolution: Fixed
          • Affects Version/s: None
          • Fix Version/s: 1.4.0-incubating
          • Component/s: None
          • Labels:
            None

            Description

            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.

              Attachments

                Activity

                  People

                  • Assignee:
                    julianhyde Julian Hyde
                    Reporter:
                    julianhyde Julian Hyde
                  • Votes:
                    0 Vote for this issue
                    Watchers:
                    4 Start watching this issue

                    Dates

                    • Created:
                      Updated:
                      Resolved: