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87 lines
3.1 KiB
Markdown
87 lines
3.1 KiB
Markdown
---
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id: topnmetricspec
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title: "TopNMetricSpec"
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---
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<!--
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~ Licensed to the Apache Software Foundation (ASF) under one
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~ or more contributor license agreements. See the NOTICE file
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~ distributed with this work for additional information
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~ regarding copyright ownership. The ASF licenses this file
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~ to you under the Apache License, Version 2.0 (the
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~ "License"); you may not use this file except in compliance
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~ with the License. You may obtain a copy of the License at
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~
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~ http://www.apache.org/licenses/LICENSE-2.0
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~
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~ Unless required by applicable law or agreed to in writing,
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~ software distributed under the License is distributed on an
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~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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~ KIND, either express or implied. See the License for the
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~ specific language governing permissions and limitations
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~ under the License.
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-->
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In Apache Druid (incubating), the topN metric spec specifies how topN values should be sorted.
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## Numeric TopNMetricSpec
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The simplest metric specification is a String value indicating the metric to sort topN results by. They are included in a topN query with:
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```json
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"metric": "<metric_name>"
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```
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The metric field can also be given as a JSON object. The grammar for dimension values sorted by numeric value is shown below:
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```json
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"metric": {
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"type": "numeric",
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"metric": "<metric_name>"
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}
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```
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|property|description|required?|
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|--------|-----------|---------|
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|type|this indicates a numeric sort|yes|
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|metric|the actual metric field in which results will be sorted by|yes|
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## Dimension TopNMetricSpec
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This metric specification sorts TopN results by dimension value, using one of the sorting orders described here: [Sorting Orders](./sorting-orders.md)
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|property|type|description|required?|
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|--------|----|-----------|---------|
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|type|String|this indicates a sort a dimension's values|yes, must be 'dimension'|
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|ordering|String|Specifies the sorting order. Can be one of the following values: "lexicographic", "alphanumeric", "numeric", "strlen". See [Sorting Orders](./sorting-orders.md) for more details.|no, default: "lexicographic"|
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|previousStop|String|the starting point of the sort. For example, if a previousStop value is 'b', all values before 'b' are discarded. This field can be used to paginate through all the dimension values.|no|
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The following metricSpec uses lexicographic sorting.
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```json
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"metric": {
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"type": "dimension",
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"ordering": "lexicographic",
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"previousStop": "<previousStop_value>"
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}
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```
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Note that in earlier versions of Druid, the functionality provided by the DimensionTopNMetricSpec was handled by two separate spec types, Lexicographic and Alphanumeric (when only two sorting orders were supported). These spec types have been deprecated but are still usable.
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## Inverted TopNMetricSpec
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Sort dimension values in inverted order, i.e inverts the order of the delegate metric spec. It can be used to sort the values in ascending order.
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```json
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"metric": {
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"type": "inverted",
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"metric": <delegate_top_n_metric_spec>
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}
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```
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|property|description|required?|
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|--------|-----------|---------|
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|type|this indicates an inverted sort|yes|
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|metric|the delegate metric spec. |yes|
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