What is the method for grouping queries in Elasticsearch?

Elasticsearch offers various methods for group queries, with the most commonly used being the use of aggregation feature.

Aggregation is a data processing method that groups documents in a collection based on specified criteria and calculates statistical information for each group. It can be used to compute various statistical indicators such as averages, maximums, minimums, and totals.

Here is a general outline of the steps for conducting a group query using Elasticsearch.

1. Create a query request, specifying the index and criteria to be searched.
2. Define one or more grouping conditions using the aggregation function. Aggregation can group based on field values, date ranges, geolocation, etc.
3. Optionally, use aggregation functions to calculate statistical information for each group, such as average, maximum, minimum, and sum.
4. Execute the query request and retrieve the results.

Here is an example of using aggregation function for grouping query:

GET /my_index/_search
{
  "size": 0,
  "aggs": {
    "group_by_field": {
      "terms": {
        "field": "my_field"
      },
      "aggs": {
        "avg_value": {
          "avg": {
            "field": "my_value"
          }
        }
      }
    }
  }
}

In this example, we first specify the index we want to query as my_index. Then, we use the terms aggregation to group documents by the values of the my_field field. Within each group, we calculate the average value of the my_value field using the avg aggregation.

Finally, we set the size to 0 to indicate that we only want to return the aggregation results without returning specific documents. After executing the query request, we will obtain the results grouped by the my_field field, including the average value of each group.