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  1. Calcite
  2. CALCITE-1828

Push the FILTER clause into Druid as a Filtered Aggregator

    Details

    • Type: Improvement
    • Status: Closed
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: 1.12.0
    • Fix Version/s: 1.14.0
    • Component/s: druid
    • Labels:
      None

      Description

      Druid has support for a special aggregator it calls the Filtered Aggregator that allows aggregations to occur with filters independent to other filters in the Druid query.

      An example where the filtered aggregator is useful:

      SELECT 
      sum("col1") FILTER (WHERE <condition1>),
      sum("col2") FILTER (WHERE <condition2>)
      FROM "table"; 
      

      Currently, calcite will scan Druid, then do the filtering and aggregation itself. With filtered aggregators, both the filter and aggregation and be pushed into Druid.

      A few comments/questions:

      1) If all conditions in the filter clause are the same, then instead of pushing filtered aggregators individually, it would make more sense to push 1 single filter into the Druid query. I.e the filters can be factored out into 1 filter. I don't see calcite currently do this, does it have such a rule in place already?

      2) The filters can/should only be pushed if they are filtering on dimension columns

      3) Currently, the above query would create the following relation:
      DruidQuery -> Project -> Aggregate. There is already a rule called DruidAggregateProjectRule which matches the previous relation. Is it better to add logic to that rule, or to create a new rule that also matches that relation?

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              • Assignee:
                zhumayun Zain Humayun
                Reporter:
                zhumayun Zain Humayun
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                • Created:
                  Updated:
                  Resolved: