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https://issues.apache.org/jira/browse/CALCITE-1787?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16025269#comment-16025269
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Zain Humayun commented on CALCITE-1787:
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[~julianhyde] I've pushed a new commit addressing your review comments. Please
let me know if I missed something or if you have any other comments. Addressing
[~bslim]s concerns, I'm currently working with [~axeisghost] to add post
aggregation support into calcite (we sit beside each other at work). Once i'm
done CALCITE-1787, i'll switch over to CALCITE-1803. Since calcite does not
currently have support for filtered aggregators, I was wondering if we should
bundle that feature in with CALCITE-1803. [~bslim] could you comment on use
cases for filtered aggregations in calcite? i.e queries in which it is
advantageous to use filtered aggregators in addition to/as opposed to regular
filters.
> thetaSketch Support for Druid Adapter
> -------------------------------------
>
> Key: CALCITE-1787
> URL: https://issues.apache.org/jira/browse/CALCITE-1787
> Project: Calcite
> Issue Type: New Feature
> Components: druid
> Affects Versions: 1.12.0
> Reporter: Zain Humayun
> Assignee: Julian Hyde
> Priority: Minor
>
> Currently, the Druid adapter does not support the
> [thetaSketch|http://druid.io/docs/latest/development/extensions-core/datasketches-aggregators.html]
> aggregate type, which is used to measure the cardinality of a column
> quickly. Many Druid instances support theta sketches, so I think it would be
> a nice feature to have.
> I've been looking at the Druid adapter, and propose we add a new DruidType
> called {{thetaSketch}} and then add logic in the {{getJsonAggregation}}
> method in class {{DruidQuery}} to generate the {{thetaSketch}} aggregate.
> This will require accessing information about the columns (what data type
> they are) so that the thetaSketch aggregate is only produced if the column's
> type is {{thetaSketch}}.
> Also, I've noticed that a {{hyperUnique}} DruidType is currently defined, but
> a {{hyperUnique}} aggregate is never produced. Since both are approximate
> aggregators, I could also couple in the logic for {{hyperUnique}}.
> I'd love to hear your thoughts on my approach, and any suggestions you have
> for this feature.
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