mirror of https://github.com/apache/druid.git
120 lines
3.2 KiB
Markdown
120 lines
3.2 KiB
Markdown
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---
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layout: doc_page
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---
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TopN queries
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==================
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TopN queries return a sorted set of results for the values in a given dimension according to some criteria. Conceptually, they can be thought of as an approximate [GroupByQuery](GroupByQuery.html) over a single dimension with an [Ordering](Ordering.html) spec. TopNs are much faster and resource efficient than GroupBys for this use case. These types of queries take a topN query object and return an array of JSON objects where each object represents a value asked for by the topN query.
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A topN query object looks like:
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```json
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"queryType": "topN",
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"dataSource": "sample_data",
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"dimension": "sample_dim",
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"threshold": 5,
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"metric": "count",
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"granularity": "all",
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"filter": {
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"type": "and",
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"fields": [
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{
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"type": "selector",
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"dimension": "dim1",
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"value": "some_value"
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},
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{
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"type": "selector",
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"dimension": "dim2",
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"value": "some_other_val"
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}
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]
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},
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"aggregations": [
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{
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"type": "longSum",
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"name": "count",
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"fieldName": "count"
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},
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{
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"type": "doubleSum",
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"name": "some_metric",
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"fieldName": "some_metric"
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}
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],
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"postAggregations": [
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{
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"type": "arithmetic",
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"name": "sample_divide",
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"fn": "/",
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"fields": [
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{
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"type": "fieldAccess",
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"name": "some_metric",
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"fieldName": "some_metric"
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},
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{
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"type": "fieldAccess",
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"name": "count",
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"fieldName": "count"
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}
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]
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}
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],
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"intervals": [
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"2013-08-31T00:00:00.000/2013-09-03T00:00:00.000"
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]
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}
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```
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There are 10 parts to a topN query, but 7 of them are shared with [TimeseriesQuery](TimeseriesQuery.html). Please review [TimeseriesQuery](TimeseriesQuery.html) for meanings of fields not defined below.
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|property|description|required?|
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|--------|-----------|---------|
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|dimension|A JSON object defining the dimension that you want the top taken for. For more info, see [DimensionSpecs](DimensionSpecs.html)|yes|
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|threshold|An integer defining the N in the topN (i.e. how many you want in the top list)|yes|
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|metric|A JSON object specifying the metric to sort by for the top list. For more info, see [TopNMetricSpec](TopNMetricSpec.html).|yes|
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Please note the context JSON object is also available for topN queries and should be used with the same caution as the timeseries case.
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The format of the results would look like so:
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```json
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[
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{
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"timestamp": "2013-08-31T00:00:00.000Z",
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"result": [
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{
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"user": "67.173.175.77",
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"count": 111,
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"some_metrics": 10669,
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"average": 96.11711711711712
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},
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{
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"user": "24.10.49.170",
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"count": 88,
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"some_metrics": 28344,
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"average": 322.09090909090907
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},
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{
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"user": "72.193.24.148",
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"count": 70,
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"some_metrics": 871,
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"average": 12.442857142857143
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},
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{
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"user": "108.46.28.47",
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"count": 62,
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"some_metrics": 815,
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"average": 13.14516129032258
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},
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{
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"user": "99.181.143.133",
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"count": 60,
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"some_metrics": 2787,
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"average": 46.45
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}
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]
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}
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]
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```
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