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https://issues.apache.org/jira/browse/PHOENIX-136?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13955500#comment-13955500
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James Taylor commented on PHOENIX-136:
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Can you list your top 5 nested queries you'd like to support, [~alexdl]?
That'll help drive this use case. [~maryannxue] is already working on this.
BTW, often times a query can be "flattened" manually. Is that not the case for
you?
> Support derived tables
> ----------------------
>
> Key: PHOENIX-136
> URL: https://issues.apache.org/jira/browse/PHOENIX-136
> Project: Phoenix
> Issue Type: Task
> Reporter: James Taylor
> Assignee: James Taylor
> Labels: enhancement
>
> Add support for derived queries of the form:
> SELECT * FROM ( SELECT company, revenue FROM Company ORDER BY revenue) LIMIT
> 10
> Adding support for this requires a compile time change as well as a runtime
> execution change. The first version of the compile-time change could limit
> aggregation to only be allowed in the inner or the outer query, but not both.
> In this case, the inner and outer queries can be combined into a single query
> with the outer select becoming just a remapping of a subset of the projection
> from the inner select. The second version of the compile-time change could
> handle aggregation in the inner and outer select by performing client side
> (this is likely a less common scenario).
> For the runtime execution, change the UngroupedAggregateRegionObserver would
> be modified to look for a new "TopNLimit" attribute with an int value in the
> Scan. This would control the maximum number of values for the coprocessor to
> hold on to as the scan is performed. Then the
> GroupedAggregatingResultIterator would be modified to handle keeping the topN
> values received back from all the child iterators.
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