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https://issues.apache.org/jira/browse/CALCITE-1787?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16039728#comment-16039728
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Joshua Walters commented on CALCITE-1787:
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[~bslim]: Yes, our Hive users use the UDFs for sketches, so they would be
familiar with that approach.
[~julianhyde]: Both approaches sound reasonable, we can move forward with
whichever you prefer.
Just to define the scope of the "alias" solution (so we know what to develop):
Taking this example: https://calcite.apache.org/docs/druid_adapter.html
There is a column {{user}}, which contains user ids. It is converted to a
metric and renamed to {{user_unique}} on Druid ingestion. What if instead of
this, it is converted to a metric but it keeps the same name {{user}}. Its type
would still be {{hyperUnique}}, but as a hyperUnique column it can only be used
in projections (with some aggregate functions like {{COUNT DISTINCT}}). If it
is used in a filter or a group by, it would throw an error as the {{user}}
column does not support such actions.
Would this work? Or am I misunderstanding what you are looking for?
> 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.
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