[GitHub] kskalski commented on issue #5566: Applying doubleSum over doubleFirst aggregations in nested groupBy fails

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kskalski commented on issue #5566: Applying doubleSum over doubleFirst aggregations in nested groupBy fails
URL: https://github.com/apache/incubator-druid/issues/5566#issuecomment-409125068
 
 
   @jihoonson thanks for the tip, indeed this makes the query work fine. I'm wondering though, if this use-case shouldn't be possible to handle automatically. In fact Druid has the concept of "finalized" and not-finalized values from aggregators and it can apply it correctly to first/last aggregators, which implement that pattern, e.g.:
   
   ```
   {
       "queryType": "groupBy",
       "dataSource": "pm_data",
       "aggregations":[{ "type": "doubleFirst", "name": "value_num", "fieldName": "value_num" }],
       "dimensions": ["counter_id"],
       "intervals": "2017-06-30T00:00:00/2017-07-02T16:46:40",
       "filters": {"type": "selector", "dimension": "version", "value": "43:48501"},
       "granularity": "day"
   }
   ```
   
   works fine returning just value num without using expression postaggregator. Shouldn't it also apply the same logic in nested query? I suppose outer query will always treat its input as finalized, so in essence the nested query should finalize its results.
   
   Actually, I would like to know how the mechanizm of finalizing results works, since I also had similar problem using Java client classes (_com.simplaex.clients.druid.DruidClient_, which I know is not supported approach, but still might shed some light on the issue here) when executing above (non-nested) group_by query - the client was not able to parse the results correctly, so I suppose there is some trick / special postprocessing / flag forcing finalization of results.

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