# 最大值桶聚合(Max Bucket Aggregation)

> 警告:此功能是实验性的，可能会在将来的版本中完全更改或删除。Elastic将采取最大的努力来解决此问题，但实验功能不受SLA官方功能的支持。

最大值桶聚合所定义的桶包含一组聚合指定度量的最大值，并且同时输出桶的键和值。指定的度量必须是数字并且这个聚合必须是多桶聚合。

## 语法 <a href="#maxbucketaggregation-yu-fa" id="maxbucketaggregation-yu-fa"></a>

`max_bucket`聚合结构如下：

```
{
    "max_bucket": {
        "buckets_path": "the_sum"
    }
}
```

`max_bucket` 参数如下：

| 参数名称          | 描述                                                                                                                                                                                                                                                                                          | 是否必填 | 默认值  |
| ------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---- | ---- |
| buckets\_path | 想要计算最大值的桶路径，点击[the section called “`buckets_path` Syntax](https://www.elastic.co/guide/en/elasticsearch/reference/5.4/search-aggregations-pipeline.html#buckets-path-syntax)[edit](https://github.com/elastic/elasticsearch/edit/5.4/docs/reference/aggregations/pipeline.asciidoc)”查看更多细节  | 必填   |      |
| gap\_policy   | 当数据缺口出现时采用的策略，点击[the section called “Dealing with gaps in the data](https://www.elastic.co/guide/en/elasticsearch/reference/5.4/search-aggregations-pipeline.html#gap-policy)[edit](https://github.com/elastic/elasticsearch/edit/5.4/docs/reference/aggregations/pipeline.asciidoc)”查看更多细节 | 可选   | skip |
| format        | 用于规范聚合输出值的格式                                                                                                                                                                                                                                                                                | 可选   | null |

以下代码段计算每月总销售额的最大值：

```
POST /sales/_search
{
    "size": 0,
    "aggs" : {
        "sales_per_month" : {
            "date_histogram" : {
                "field" : "date",
                "interval" : "month"
            },
            "aggs": {
                "sales": {
                    "sum": {
                        "field": "price"
                    }
                }
            }
        },
        "max_monthly_sales": {
            "max_bucket": {
                "buckets_path": "sales_per_month>sales" #1
            }
        }
    }
}
```

| 1 | buckets\_path指示这个max\_bucket聚合是要得到sales\_per\_month日期直方图中sales聚合的最大值。 |
| - | --------------------------------------------------------------------- |

可能得到如下的响应：

```
{
   "took": 11,
   "timed_out": false,
   "_shards": ...,
   "hits": ...,
   "aggregations": {
      "sales_per_month": {
         "buckets": [
            {
               "key_as_string": "2015/01/01 00:00:00",
               "key": 1420070400000,
               "doc_count": 3,
               "sales": {
                  "value": 550.0
               }
            },
            {
               "key_as_string": "2015/02/01 00:00:00",
               "key": 1422748800000,
               "doc_count": 2,
               "sales": {
                  "value": 60.0
               }
            },
            {
               "key_as_string": "2015/03/01 00:00:00",
               "key": 1425168000000,
               "doc_count": 2,
               "sales": {
                  "value": 375.0
               }
            }
         ]
      },
      "max_monthly_sales": {
          "keys": ["2015/01/01 00:00:00"], #1
          "value": 550.0
      }
   }
}
```

| 1 | key是字符串数组，因为最大值可能存在于多个存储桶中 |
| - | -------------------------- |


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