[source, ruby]
----
response = client.search(
  index: 'sales',
  body: {
    size: 0,
    aggregations: {
      sales_per_month: {
        date_histogram: {
          field: 'date',
          calendar_interval: 'month'
        },
        aggregations: {
          sales: {
            sum: {
              field: 'price'
            }
          },
          sales_deriv: {
            derivative: {
              buckets_path: 'sales',
              unit: 'day'
            }
          }
        }
      }
    }
  }
)
puts response
----
