When you perform a range aggregation in Elasticsearch, it groups documents based on a numeric or date field and counts the number of documents that fall within a specified range or set of ranges.
To perform a range aggregation, you first specify the name of the field you want to aggregate on, and then define one or more ranges. Each range is defined by a minimum value, a maximum value, and a boolean flag indicating whether the range is inclusive or exclusive.
When Elasticsearch executes the range aggregation, it sorts the documents based on the specified field and then iterates over them one at a time. For each document, Elasticsearch checks if the value of the specified field falls within each of the defined ranges. If the value falls within a range, Elasticsearch increments the count for that range.
Once Elasticsearch has processed all of the documents, it returns a histogram with the number of documents that fall into each range.
For example, let’s say you have an index of products, and each document has a “price” field that represents the price of the product. You could perform a range aggregation on the “price” field with two ranges: one for products that cost less than $50, and one for products that cost $50 or more. Elasticsearch would then sort the products by price, iterate over them one at a time, and count the number of products that fall into each range.
You can also perform range aggregations on date fields. In this case, Elasticsearch converts the date values to numeric values using a specified date format, and then performs the aggregation in the same way as for numeric fields.
Range aggregations can be a powerful tool for analyzing and understanding your data. By grouping documents into meaningful categories based on numeric or date values, you can quickly gain insights into patterns and trends in your data.