[jira] [Commented] (CALCITE-1828) Push the FILTER clause into Druid as a Filtered Aggregator

["slim bouguerra (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-1828?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16035305#comment-16035305 ] 

slim bouguerra commented on CALCITE-1828:
-----------------------------------------

I agree on 1 if it is doable. Also i would like to see (if possible) to have an OR of the filter to be added upfront as first Filter. That will act as a first pruning filter to select the rows needed for the aggregation then will do the rest as `Filtered aggregator`. Taking a simple case where cond1 is country=US, cond2 is country=CA, The first filter will be country = US OR country = CA. 
Again i feel like with arbitrary filter expression might be hard to construct such filter but maybe calcite can do that.

2 -> yes, i thought we already do this.

3 -> not sure maybe [~julianhyde] or [~jcamachorodriguez] can answer.   

> Push the FILTER clause into Druid as a Filtered Aggregator 
> -----------------------------------------------------------
>
>                 Key: CALCITE-1828
>                 URL: https://issues.apache.org/jira/browse/CALCITE-1828
>             Project: Calcite
>          Issue Type: Improvement
>          Components: druid
>    Affects Versions: 1.12.0
>            Reporter: Zain Humayun
>            Assignee: Zain Humayun
>
> Druid has support for a special aggregator it calls the [Filtered Aggregator|http://druid.io/docs/latest/querying/aggregations.html] that allows aggregations to occur with filters independent to other filters in the Druid query.
> An example where the filtered aggregator is useful:
> {code:sql}
> SELECT 
> sum("col1") FILTER (WHERE <condition1>),
> sum("col2") FILTER (WHERE <condition2>)
> FROM "table"; 
> {code} 
> 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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