Sorting (topN)

Sorting (topN)

Apache Druid supports two query languages: Druid SQL and native queries. This document describes the native language. For information about sorting in SQL, refer to the SQL documentation.

In Apache Druid, the topN metric spec specifies how topN values should be sorted.

Numeric TopNMetricSpec

The simplest metric specification is a String value indicating the metric to sort topN results by. They are included in a topN query with:

"metric": "<metric_name>"

The metric field can also be given as a JSON object. The grammar for dimension values sorted by numeric value is shown below:

"metric": {
    "type": "numeric",
    "metric": "<metric_name>"
}

property	description	required?
type	this indicates a numeric sort	yes
metric	the actual metric field in which results will be sorted by	yes

Dimension TopNMetricSpec

This metric specification sorts TopN results by dimension value, using one of the sorting orders described here: Sorting Orders

property	type	description	required?
type	String	this indicates a sort a dimension’s values	yes, must be ‘dimension’
ordering	String	Specifies the sorting order. Can be one of the following values: “lexicographic”, “alphanumeric”, “numeric”, “strlen”. See Sorting Orders for more details.	no, default: “lexicographic”
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

The following metricSpec uses lexicographic sorting.

"metric": {
    "type": "dimension",
    "ordering": "lexicographic",
    "previousStop": "<previousStop_value>"
}

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.

Inverted TopNMetricSpec

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.

"metric": {
    "type": "inverted",
    "metric": <delegate_top_n_metric_spec>
}

property	description	required?
type	this indicates an inverted sort	yes
metric	the delegate metric spec.	yes