所以我发现https://www.elastic.co/guide/en/elasticsearch/reference/7.x/search-aggregations-bucket-filter-aggregation.html 只需添加一个子聚合，或者在bucket聚合中添加另一个聚合，就可以获得除 doc_count 在桶里。
举个例子：

POST /sales/_search?size=0
{
    "aggs" : {
        "sales_over_time" : {
            "date_histogram" : {
                "field" : "date",
                "calendar_interval" : "month"
            },
            "aggs" : {
                "avg_price" : { "avg" : { "field" : "price" } }
            }
        }
    }
}