[GitHub] [incubator-pinot] kkrugler opened a new issue #6676: Support multiple columns in distinct count aggregations

[GitBox <gi...@apache.org>]

kkrugler opened a new issue #6676:
URL: https://github.com/apache/incubator-pinot/issues/6676


   Currently these [Pinot aggregations](https://docs.pinot.apache.org/users/user-guide-query/supported-aggregations) only work with a single column:
   
   - DISTINCTCOUNT
   - DISTINCTCOUNTHLL
   - DISTINCTCOUNTRAWHLL
   - DistinctCountThetaSketch
   - DistinctCountRawThetaSketch
   - DISTINCTCOUNTMV
   - DISTINCTCOUNTHLLMV
   - DISTINCTCOUNTRAWHLLMV
   
   This becomes a problem when you need to get the count of the total number of groups from an aggregation (e.g. to support deeper paging in the dashboard UI), and more than one column is being used for grouping. For example, the query `select advertiser,publisher,sum(adSpend) from table group by advertiser,publisher order by sum(adSpend) desc limit 1000` is using two columns (`advertiser,publisher`) for grouping.
   
   The current workaround is do use `concat` to build a single key, e.g. `select distinctcounthll(concat(advertiser, publisher, '|')) from table`, but that suffers from the performance penalty of using the `concat` scalar UDF.
   


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