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Julian Hyde commented on CALCITE-1787: -------------------------------------- Both of the following queries are valid SQL and we should push them down to Druid and use theta sketches (or HLL, whichever is available): {code} select count(distinct "customer_id") from "foodmart" where "store_city" in ('Chicago', 'Seattle') select count(distinct "customer_id") filter (where "store_city" in ('Chicago', 'Seattle') from "foodmart" {code} That's the what. Now let's figure out the how. > 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: Zain Humayun > 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. -- This message was sent by Atlassian JIRA (v6.3.15#6346)