I think it's not necessary, though I was just following [cardinality aggregator](https://github.com/apache/incubator-druid/blob/master/processing/src/main/java/org/apache/druid/query/aggregation/cardinality/types/CardinalityAggregatorColumnSelectorStrategyFactory.java).
[ Full content available at: https://github.com/apache/incubator-druid/pull/6397 ] This message was relayed via gitbox.apache.org for devnull@infra.apache.org
