Executing an aggregation

ElasticSearch provides several functionalities other than search; it allows executing statistics and real-time analytics on searches via aggregations.

Getting ready

You need a working ElasticSearch cluster and an index populated with the script, which is available at https://github.com/aparo/elasticsearch-cookbook-second-edition.

How to do it...

To execute an aggregation, we will perform the steps given as follows:

1. From the command line, we can execute a query with aggregations:

   curl -XGET 'http://127.0.0.1:9200/test-index/test-type/_search?pretty=true&size=0' -d '{
     "query": {
       "match_all": {}
     },
     "aggregations": {
       "tag": {
         "terms": {
           "field": "tag",
           "size": 10
         }
       }
     }
   }'
   

   In this case, we have used a match_all query plus a terms aggregation that is used to count terms.

2. The result returned by ElasticSearch, if everything is...