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https://issues.apache.org/jira/browse/DRILL-28?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Timothy Chen reassigned DRILL-28:
---------------------------------
Assignee: Timothy Chen
> Implement CollapseAggregate Reference Operator
> ----------------------------------------------
>
> Key: DRILL-28
> URL: https://issues.apache.org/jira/browse/DRILL-28
> Project: Apache Drill
> Issue Type: New Feature
> Reporter: Timothy Chen
> Assignee: Timothy Chen
> Labels: logical
>
> CollapseAggregate (1)
> The collapse aggregate operator collapses a segment of records into a single
> record. In the case that a segment (within) is undefined, the collapse
> aggregate will collapse all input records into a single output record.
> The only outputs of the collapse aggregate operator are the provided
> aggregations and the values defined as carryover. The collapse aggregate
> operator also can be provided a target field reference with which to select
> the record used for carryover values.
> In the case that a target reference is undefined, the collapse aggregate
> operation will be free to choose which record the carryover values are drawn
> from (typically, this is because all records share the same value). In the
> case that a target field reference is provided, will draw the carryover
> variables from a record where the target field references has a true value.
> If more than one record has a target field value that is true, the carryover
> values will be drawn from one of those records. In the case that no record
> within the target segment has a target value of true, no record will be
> emitted from that target segment. In no case will more than one record be
> emitted per segment.
> { @id†: <opref>, op: “collapsingaggregate”,
> input†: <input>,
> within*: <name>,
> target*: <name>,
> carryover: [<name>, … , <name>],
> aggregations: [
> {ref: <name>, expr: <aggexpr> },...
> ]
> }
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