Learning Elastic Stack 6.0

Cardinality aggregation

Finding the count of unique elements can be done with the cardinality aggregation. It is similar to finding the result of a query such as the following:

select count(*) from (select distinct username from usageReport) u;

Finding the cardinality or the number of unique values for a specific field is a very common requirement. If you have click-stream from the different visitors on your website, you may want to find out how many unique visitors you got in a given day, week, or month.

Let us understand how we find out the count of unique users for which we have network traffic data:

GET bigginsight/_search{ "aggregations": {    "unique_visitors": {      "cardinality": {        "field": "username"      }    }  },  "size": 0}

The cardinality aggregation ...