# 全局聚合(Global Aggregation)

定义搜索执行上下文中的所有文档的单个bucket，这个上下文由索引和您正在搜索的文档类型定义，但不受搜索查询本身的影响。

> 全局聚合器只能作为顶层聚合器放置，因为将全局聚合器嵌入到另一个分组聚合器中是没有意义的。

例子：

```
POST /sales/_search?size=0
{
    "query" : {
        "match" : { "type" : "t-shirt" }
    },
    "aggs" : {
        "all_products" : {
            "global" : {}, ＃1
            "aggs" : {  ＃2
                "avg_price" : { "avg" : { "field" : "price" } }
            }
        },
        "t_shirts": { "avg" : { "field" : "price" } }
    }
}
```

\#1 global aggregation(全局聚合)有一个空的体

\#2 为这个global aggregation(全局聚合)注册的子聚合

上面的聚合演示了如何在搜索上下文中的所有文档上计算聚合(本例中的avg\_price),无论查询如何（在我们的示例中，它将计算我们目录中所有产品的平均价格，而不仅仅是在“shirts”）

上述聚合的响应结果：

```
{
    ...
    "aggregations" : {
        "all_products" : {
            "doc_count" : 7, ＃1
            "avg_price" : {
                "value" : 140.71428571428572  ＃2
            }
        },
        "t_shirts": {
            "value" : 128.33333333333334  ＃3
        }
    }
}
```

＃1 汇总的文档数量（在我们的例子中，搜索范围内的所有文档）

＃2 所有产品的平均价格

＃3 所有“t\_shirts”的平均价格


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