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add documentation for group by array based result format (#8416)

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Clint Wylie 2019-08-28 08:30:31 -07:00 committed by Gian Merlino
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commit 3baf31e9a8
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docs/querying/groupbyquery.md
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@ -442,3 +442,19 @@ Supported query contexts:
|`maxIntermediateRows`|Can be used to lower the value of `druid.query.groupBy.maxIntermediateRows` for this query.|None| |`maxIntermediateRows`|Can be used to lower the value of `druid.query.groupBy.maxIntermediateRows` for this query.|None|
|`maxResults`|Can be used to lower the value of `druid.query.groupBy.maxResults` for this query.|None| |`maxResults`|Can be used to lower the value of `druid.query.groupBy.maxResults` for this query.|None|
|`useOffheap`|Set to true to store aggregations off-heap when merging results.|false| |`useOffheap`|Set to true to store aggregations off-heap when merging results.|false|
##### Array based result rows
Internally Druid always uses an array based representation of groupBy result rows, but by default this is translated
into a map based result format at the Broker. To reduce the overhead of this translation, results may also be returned
from the Broker directly in the array based format if `resultAsArray` is set to `true` on the query context.
Each row is positional, and has the following fields, in order:
* Timestamp (optional; only if granularity != ALL)
* Dimensions (in order)
* Aggregators (in order)
* Post-aggregators (optional; in order, if present)
This schema is not available on the response, so it must be computed from the issued query in order to properly read
the results.