ES常用知识点整理第一部分

• 引言
• API
• • Crud API
  • Bulk API
  • 批量读取
  • 批量查询
  • ES服务器常见错误返回
  • 倒排索引
  • 分词器
  • • 中文分词器
• Search API
• • URI Search
  • Query DSL
  • • 查询表达式
    • 短语搜索
    • Query String 和 Simple Query String
• mapping映射
• • 动态映射
  • 手动映射
  • • 多字段特性
    • 自定义分词
• Index Template
• Dynamic Template
• 聚合
• 小结

---

引言

本文列举的es用法可能不全或者不清楚，具体建议参考官方文档:

https://www.elastic.co/guide/index.html

---

API

Crud API

• create一个文档

#创建索引,不指定mapping,会在添加第一条文档时,自动解析形成mapping
PUT /stu
{
  "settings": {
    "number_of_shards": 1, 
    "number_of_replicas": 0 
  }
}

#添加文档---id存在,则添加失败
put /stu/_create/1
{
   "name":"大忽悠",
   "age":18
}

#添加文档--随机生成文档id
post /stu/_doc
{
   "name":"小朋友",
   "age":20
}

• get一个文档

#获取文档
get /stu/_doc/1
get /stu/_doc/dM_04YUB7nCycfEBpay0

#查询结果
{
  "_index" : "stu",
  "_type" : "_doc",
  "_id" : "1",
  "_version" : 1,
  "_seq_no" : 0,
  "_primary_term" : 1,
  "found" : true,
  "_source" : {
    "name" : "大忽悠",
    "age" : 18
  }
}

{
  "_index" : "stu",
  "_type" : "_doc",
  "_id" : "dM_04YUB7nCycfEBpay0",
  "_version" : 1,
  "_seq_no" : 1,
  "_primary_term" : 1,
  "found" : true,
  "_source" : {
    "name" : "小朋友",
    "age" : 20
  }
}

• index 索引一个文档 ，可以看做: save or delete update

#索引一个文档
put /stu/_doc/1 
{
   "name":"dhy",
   "age":21
}

#索引结果
{
  "_index" : "stu",
  "_type" : "_doc",
  "_id" : "1",
  "_version" : 3,
  "result" : "updated",
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "failed" : 0
  },
  "_seq_no" : 3,
  "_primary_term" : 1
}

• update文档

#更新一个文档
post /stu/_update/1
{
  "doc":{
    "name":"大忽悠和小朋友"
  }
}

#更新结果
{
  "_index" : "stu",
  "_type" : "_doc",
  "_id" : "1",
  "_version" : 4,
  "result" : "noop",
  "_shards" : {
    "total" : 0,
    "successful" : 0,
    "failed" : 0
  },
  "_seq_no" : 4,
  "_primary_term" : 1
}

---

Bulk API

#批量操作
post _bulk
{"index":{"_index":"stu","_id":"3"}}
{"name":"张三","age":20}
{"delete":{"_index":"stu","_id":"1"}}
{"create":{"_index":"stu","_id":"4"}}
{"name":"李四","age":21}
{"update":{"_index":"stu","_id":"4"}}
{"doc":{"age":25}}

#结果
{
  "took" : 2,
  "errors" : true,
  "items" : [
    {
      "index" : {
        "_index" : "stu",
        "_type" : "_doc",
        "_id" : "3",
        "_version" : 4,
        "result" : "updated",
        "_shards" : {
          "total" : 1,
          "successful" : 1,
          "failed" : 0
        },
        "_seq_no" : 13,
        "_primary_term" : 1,
        "status" : 200
      }
    },
    {
      "delete" : {
        "_index" : "stu",
        "_type" : "_doc",
        "_id" : "1",
        "_version" : 2,
        "result" : "not_found",
        "_shards" : {
          "total" : 1,
          "successful" : 1,
          "failed" : 0
        },
        "_seq_no" : 14,
        "_primary_term" : 1,
        "status" : 404
      }
    },
    {
      "create" : {
        "_index" : "stu",
        "_type" : "_doc",
        "_id" : "4",
        "status" : 409,
        "error" : {
          "type" : "version_conflict_engine_exception",
          "reason" : "[4]: version conflict, document already exists (current version [2])",
          "index_uuid" : "Oh7Ujc5tSgS5KzsFqIXf5g",
          "shard" : "0",
          "index" : "stu"
        }
      }
    },
    {
      "update" : {
        "_index" : "stu",
        "_type" : "_doc",
        "_id" : "4",
        "_version" : 2,
        "result" : "noop",
        "_shards" : {
          "total" : 1,
          "successful" : 1,
          "failed" : 0
        },
        "_seq_no" : 12,
        "_primary_term" : 1,
        "status" : 200
      }
    }
  ]
}

---

批量读取

#批量读取
get _mget
{
  "docs":[
    {
      "_index":"stu",
      "_id":1
    },
    {
      "_index":"stu",
      "_id":3
    }
  ]
}

#结果
{
  "docs" : [
    {
      "_index" : "stu",
      "_type" : "_doc",
      "_id" : "1",
      "found" : false
    },
    {
      "_index" : "stu",
      "_type" : "_doc",
      "_id" : "3",
      "_version" : 4,
      "_seq_no" : 13,
      "_primary_term" : 1,
      "found" : true,
      "_source" : {
        "name" : "张三",
        "age" : 20
      }
    }
  ]
}

---

批量查询

#批量查询--格式为header boby,header为空,也需要保留
post stu/_msearch
{}
{"query":{"match_all":{}},"from":0,"size":10}
{"index":"shop"}
{"query":{"match_all":{}}}

---

ES服务器常见错误返回

---

倒排索引

• 正排索引: 文档ID到文档内容和单词的关联
• 倒排索引: 单词到文档Id的关系

平时使用的mysql数据库通常都是根据ID定位一条记录的，而对于搜索引擎而，往往需要根据某个内容，定位到具体的文档ID

• 倒排索引核心组成

我画了一张简图如下:

• TF(term frequency): 单词在文档中出现的次数。
• Pos: 单词在文档中出现的位置。

第三列倒排索引包含的信息为(文档ID，单词频次，<单词位置>)，比如单词“乔布斯”对应的倒排索引里的第一项(1;1;<1>)意思是，文档1包含了“乔布斯”，并且在这个文档中只出现了1次，位置在第一个。

es的JSON文档中每个字段,都有自己的倒排索引，我们可以指定某些字段不做索引:

• 优点: 节省存储空间
• 缺点: 字段无法被搜索

---

分词器

• 分词器组成

• es内置分词器

• _analyzer API

• es内置分词器

---

中文分词器

---

Search API

---

URI Search

q：指定查询的语句，语法为 Query String Syntax
df（default field）：q 中不指定字段时，默认查询的字段，如果不指定，es 会查询所有字段
sort：排序
timeout：指定超时时间，默认不超时
from，size：用于分页

//查询 user 字段包含 seina 的文档，结果按照 age 升序排列，返回第 5～15 个文档
//如果超过 1s 没有结束，则以超时结束
GET /my_index/_search?q=seina&df=user&sort=age:asc&from=4&size=10&timeout=1s

• 指定字段查询和泛查询 (phrase是短语的意思)
  
• 泛查询：表示不指定字段查询，而是在所有字段中匹配
• term: 指定字段查询， 语法是：《 字段名:要查询的值 》

//表示 seina 或 gao，只包含某一个就符合查询需求
seina gao

//表示词语查询，要求先后顺序，必须是 seina gao 连起来才可以
"seina gao"

• Group 分组设定， 使用括号指定匹配的优先级规则

//表示必须先判断前面括号里的，再判断后面的
(quick OR brown) AND fox 
 
//表示 status 字段的值是 active 或者 pending
//如果不加括号，status:active OR pending 表示 status 字段的值是 active 或者全部字段的值是 pending
//因为 es 如果不指定字段，可能会按全部字段去匹配
status:(active OR pending) 

//可以包含 tom 但不要有 lee
username:(tom NOT lee)

//下面两个都表示可以包含 tom，一定包含 lee，也一定不包含 seina
//由此可见 ➕➖可以简化查询语句写法
username:(tom +lee -seina)
username:((lee && !seina) || (tom && lee && !seina))

注意➕在 url 中会被解析成空格，要使用 encode 后的结果，就是 %2B

age:[1 TO 10] //表示 1 <= age <= 10
age:[1 TO 10} //表示 1 <= age < 10
age:[1 TO ]  //表示 age >= 10
age:[* TO 10] //表示 age <= 10

age:>= 1
age:(>= 1 && <= 10) 或者 age:(+ >= 10 + <= 10)

name:t?m
name:tom*

name:roam~1 //表示匹配与 roam 差 1 个 character 的词，比如 foam roams 等
//以 term 为单位进行差异比较，允许在 quick 和 fox 之间插入一个词，比如 “quick fox”“quick brown fox” 都会被匹配 
"quick fox"~1 

---

Query DSL

Elasticsearch（es）大多数脚本都围绕指定文档字段数据来使用，可以 doc[‘field_name’] 形式来访问文档内指定字段数据。值得注意的是，只针对简单的值生效（数值类型字段或者不分词字段）。

post /products/_search
{
  "profile":true,
  "from": 10,
  "size":10,
  "sort":[{"price":"desc"}],
  "_source":["title","description"],
  "script_fields":{
    "desc":{
      "script":{
        "lang": "painless",
        "source":"'商品价钱为'+ doc['price']"
      }
    }
  },
  "query":{
    "match_all": {}
  }
}

---

查询表达式

• products索引的mapping信息

{
  "products" : {
    "mappings" : {
      "properties" : {
        "_class" : {
          "type" : "text"
        },
        "description" : {
          "type" : "text",
          "analyzer" : "ik_max_word"
        },
        "id" : {
          "type" : "long"
        },
        "price" : {
          "type" : "float"
        },
        "sku" : {
          "type" : "long"
        },
        "title" : {
          "type" : "text",
          "analyzer" : "ik_max_word"
        }
      }
    }
  }
}

• 如果查询时不指定分词器,那么会使用字段mapping映射中设置的分词器，默认为标准分词器

post /products/_search
{
  "profile":true,
  "sort":[{"price":"desc"}],
  "_source":["title","price","description"],
  "query":{
    "match": {
      "description": "甄选 享受"
    }
  }
}

• 查询时指定采用的分词器:

post /products/_search
{
  "profile":true,
  "sort":[{"price":"desc"}],
  "_source":["title","price","description"],
  "query":{
    "match": {
      "description": {
        "query": "甄选 享受",
        "analyzer": "standard"
      }
    }
  }
}

• 要满足所有分词条件

post /products/_search
{
  "profile":true,
  "sort":[{"price":"desc"}],
  "_source":["title","price","description"],
  "query":{
    "match": {
      "description": {
        "query": "甄选服务"
        , "operator": "and"
      }
    }
  }
}

甄选服务会被ik_max_word分词器拆分为两个词,此时and条件要求对应的description字段包含全部分词结果:

---

短语搜索

post /products/_search
{
  "profile":true,
  "sort":[{"price":"desc"}],
  "_source":["title","price","description"],
  "query":{
    "match_phrase": {
      "description": {
        "query": "甄选 品味"
        ,"slop": 1
      }
    }
  }
}

甄选 品味 被ik_max_word分词器拆分后会得到两个单词甄选和品味，match_phrase要求两个单词前后顺序保持一致，slop允许两个短语之间插入一个字符:

---

Query String 和 Simple Query String

post /products/_search
{
  "profile":true,
  "sort":[{"price":"desc"}],
  "_source":["title","price","description"],
  "query":{
    "query_string": {
       #指定默认查询字段
       "default_field": "description",
       "query": "甄选 AND 品味"
    }
  }
}

---

post /products/_search
{
  "profile":true,
  "sort":[{"price":"desc"}],
  "_source":["title","price","description"],
  "query":{
    "simple_query_string": {
       "fields": ["description"],
       "query": "甄选 AND 品味"
    }
  }
}

post /products/_search
{
  "profile":true,
  "sort":[{"price":"desc"}],
  "_source":["title","price","description"],
  "query":{
    "simple_query_string": {
       "fields": ["description"],
       "query": "甄选 AND 品味",
       "default_operator": "AND"
    }
  }
}

---

mapping映射

动态映射

• 数字用引号，默认当TEXT
• 日期格式会推导成Date
• 有一些类型会推导出错,例如地理位置信息

#写入文档，查看 Mapping
PUT mapping_test/_doc/1
{
  "firstName":"Chan",
  "lastName": "Jackie",
  "loginDate":"2018-07-24T10:29:48.103Z"
}

#查看 Mapping文件
GET mapping_test/_mapping

#Delete index
DELETE mapping_test

#dynamic mapping，推断字段的类型
PUT mapping_test/_doc/1
{
    "uid" : "123",
    "isVip" : false,
    "isAdmin": "true",
    "age":19,
    "heigh":180
}

#查看 Dynamic
GET mapping_test/_mapping

---

#默认Mapping支持dynamic，写入的文档中加入新的字段
PUT dynamic_mapping_test/_doc/1
{
  "newField":"someValue"
}

#该字段可以被搜索，数据也在_source中出现
POST dynamic_mapping_test/_search
{
  "query":{
    "match":{
      "newField":"someValue"
    }
  }
}

#修改为dynamic false
PUT dynamic_mapping_test/_mapping
{
  "dynamic": false
}

#新增 anotherField
PUT dynamic_mapping_test/_doc/10
{
  "anotherField":"someValue"
}


#该字段不可以被搜索，因为dynamic已经被设置为false
POST dynamic_mapping_test/_search
{
  "query":{
    "match":{
      "anotherField":"someValue"
    }
  }
}

get dynamic_mapping_test/_doc/10

• 新增字段信息会出现在source中
  

#修改为strict
PUT dynamic_mapping_test/_mapping
{
  "dynamic": "strict"
}



#写入数据出错，HTTP Code 400
PUT dynamic_mapping_test/_doc/12
{
  "lastField":"value"
}

DELETE dynamic_mapping_test

---

手动映射

#设置 index 为 false
DELETE users

PUT users
{
    "mappings" : {
      "properties" : {
        "firstName" : {
          "type" : "text"
        },
        "lastName" : {
          "type" : "text"
        },
        "mobile" : {
          "type" : "text",
          "index": false
        }
      }
    }
}

PUT users/_doc/1
{
  "firstName":"Ruan",
  "lastName": "Yiming",
  "mobile": "12345678"
}

POST /users/_search
{
  "query": {
    "match": {
      "mobile":"12345678"
    }
  }
}

---

#设定Null_value

DELETE users
PUT users
{
    "mappings" : {
      "properties" : {
        "firstName" : {
          "type" : "text"
        },
        "lastName" : {
          "type" : "text"
        },
        "mobile" : {
          "type" : "keyword",
          "null_value": "NULL"
        }

      }
    }
}

PUT users/_doc/1
{
  "firstName":"Ruan",
  "lastName": "Yiming",
  "mobile": null
}


PUT users/_doc/2
{
  "firstName":"Ruan2",
  "lastName": "Yiming2"

}

GET users/_search
{
  "query": {
    "match": {
      "mobile":"NULL"
    }
  }

}

---

#设置 Copy to
DELETE users
PUT users
{
  "mappings": {
    "properties": {
      "firstName":{
        "type": "text",
        "copy_to": "fullName"
      },
      "lastName":{
        "type": "text",
        "copy_to": "fullName"
      }
    }
  }
}
PUT users/_doc/1
{
  "firstName":"Ruan",
  "lastName": "Yiming"
}

GET users/_search?q=fullName:(Ruan Yiming)

POST users/_search
{
  "query": {
    "match": {
       "fullName":{
        "query": "Ruan Yiming",
        "operator": "and"
      }
    }
  }
}

---

#数组类型
PUT users/_doc/1
{
  "name":"onebird",
  "interests":"reading"
}

PUT users/_doc/1
{
  "name":"twobirds",
  "interests":["reading","music"]
}

POST users/_search
{
  "query": {
		"match_all": {}
	}
}

GET users/_mapping

• 文档source只包含新增时标注的字段

---

多字段特性

官网的解释更加明白

多字段作用通常有如下几个:

• text类型字段用于分词,进行全文索引
• 子字段类型为keyWord用于排序,聚合或者精确匹配
• 可以对一个字段采用不同的分词方式,以此实现更好的相关性

PUT my-index-000001
{
  "mappings": {
    "properties": {
      "city": {
        "type": "text",
        "fields": {
          "raw": { 
            "type":  "keyword"
          }
        }
      }
    }
  }
}

PUT my-index-000001/_doc/1
{
  "city": "New York"
}

PUT my-index-000001/_doc/2
{
  "city": "York"
}

GET my-index-000001/_search
{
  "query": {
    "match": {
      "city": "york" 
    }
  },
  "sort": {
    "city.raw": "asc" 
  },
  "aggs": {
    "Cities": {
      "terms": {
        "field": "city.raw" 
      }
    }
  }
}

DELETE m
PUT my-index-000001
{
  "mappings": {
    "properties": {
      "text": { 
        "type": "text",
        "fields": {
          "english": { 
            "type":     "text",
            "analyzer": "english"
          }
        }
      }
    }
  }
}

PUT my-index-000001/_doc/1
{ "text": "quick brown fox" } 

PUT my-index-000001/_doc/2
{ "text": "quick brown foxes" } 

GET my-index-000001/_search
{
  "query": {
    "multi_match": {
      "query": "quick brown foxes",
      "fields": [ 
        "text",
        "text.english"
      ],
      "type": "most_fields" 
    }
  }
}

如何利用多字段特性实现拼音搜索

---

自定义分词

PUT logs/_doc/1
{"level":"DEBUG"}

GET /logs/_mapping

POST _analyze
{
  "tokenizer":"keyword",
  "char_filter":["html_strip"],
  "text": "<b>hello world</b>"
}

POST _analyze
{
  "tokenizer":"path_hierarchy",
  "text":"/user/ymruan/a/b/c/d/e"
}

#使用char filter进行替换
POST _analyze
{
  "tokenizer": "standard",
  "char_filter": [
      {
        "type" : "mapping",
        "mappings" : [ "- => _"]
      }
    ],
  "text": "123-456, I-test! test-990 650-555-1234"
}

//char filter 替换表情符号
POST _analyze
{
  "tokenizer": "standard",
  "char_filter": [
      {
        "type" : "mapping",
        "mappings" : [ ":) => happy", ":( => sad"]
      }
    ],
    "text": ["I am felling :)", "Feeling :( today"]
}

// white space and snowball
GET _analyze
{
  "tokenizer": "whitespace",
  "filter": ["stop","snowball"],
  "text": ["The gilrs in China are playing this game!"]
}

snowball token filter ，它可以把 sing/ sings / singing 都转化词干 sing。不管用户搜 sing、sings、singing， 他的搜索结果都是基于「sing」这个term，所得的结果集都一样。

// whitespace与stop
GET _analyze
{
  "tokenizer": "whitespace",
  "filter": ["stop","snowball"],
  "text": ["The rain in Spain falls mainly on the plain."]
}

//remove 加入lowercase后，The被当成 stopword删除
GET _analyze
{
  "tokenizer": "whitespace",
  "filter": ["lowercase","stop","snowball"],
  "text": ["The gilrs in China are playing this game!"]
}

//正则表达式
GET _analyze
{
  "tokenizer": "standard",
  "char_filter": [
      {
        "type" : "pattern_replace",
        "pattern" : "http://(.*)",
        "replacement" : "$1"
      }
    ],
    "text" : "http://www.elastic.co"
}

---

自定义分词器:

PUT /my_index
{
    "settings": {
        "analysis": {
            "char_filter": { ... custom character filters ... },//字符过滤器
            "tokenizer":   { ...    custom tokenizers     ... },//分词器
            "filter":      { ...   custom token filters   ... },  //词单元过滤器
            "analyzer":    { ...    custom analyzers      ... }
        }
    }
}
============================实例===========================
PUT /my_index
{
    "settings": {
        "analysis": {
            "char_filter": {
                "&_to_and": {
                    "type":       "mapping",
                    "mappings": [ "&=> and "]
            }},
            "filter": {
                "my_stopwords": {
                    "type":       "stop",
                    "stopwords": [ "the", "a" ]
            }},
            "analyzer": {
                "my_analyzer": {
                    "type":         "custom",
                    "char_filter":  [ "html_strip", "&_to_and" ],
                    "tokenizer":    "standard",
                    "filter":       [ "lowercase", "my_stopwords" ]
            }}
}}}


============================实例===========================
比如自定义好的analyzer名字是my_analyzer,在此索引下的某个新增字段应用此分析器
PUT /my_index/_mapping
{
   "properties":{
        "username":{
             "type":"text",
              "analyzer" : "my_analyzer"
         },
        "password" : {
          "type" : "text"
        }
    
  }
}
=================插入数据====================
PUT /my_index/_doc/1
{
  "username":"The quick & brown fox ",
   "password":"The quick & brown fox "


}
====username采用自定义分析器my_analyzer,password采用默认的standard分析器==
===验证
GET /index_v1/_analyze
{
  "field":"username",
  "text":"The quick & brown fox"
}

GET /index_v1/_analyze
{
  "field":"password",
  "text":"The quick & brown fox"
}

---

Index Template

#数字字符串被映射成text，日期字符串被映射成日期
PUT ttemplate/_doc/1
{
	"someNumber":"1",
	"someDate":"2019/01/01"
}
GET ttemplate/_mapping

#Create a default template
PUT _template/template_default
{
  #应用到哪些索引上 
  "index_patterns": ["*"],
  "order" : 0,
  "version": 1,
  "settings": {
    "number_of_shards": 1,
    "number_of_replicas":1
  }
}


PUT /_template/template_test
{
    "index_patterns" : ["test*"],
    "order" : 1,
    "settings" : {
    	"number_of_shards": 1,
        "number_of_replicas" : 2
    },
    "mappings" : {
         #关闭符合日期格式字符串到日期类型的自动转换
    	"date_detection": false,
    	#开启对数值类型的字符串的探测
    	"numeric_detection": true
    }
}

#查看template信息
GET /_template/template_default
GET /_template/temp*

#写入新的数据，index以test开头
PUT testtemplate/_doc/1
{
	"someNumber":"1",
	"someDate":"2019/01/01"
}
GET testtemplate/_mapping
get testtemplate/_settings

PUT testmy
{
	"settings":{
		"number_of_replicas":5
	}
}

put testmy/_doc/1
{
  "key":"value"
}

get testmy/_settings
DELETE testmy
DELETE /_template/template_default
DELETE /_template/template_test

---

Dynamic Template

#Dynaminc Mapping 根据类型和字段名
DELETE my_index

PUT my_index/_doc/1
{
  "firstName":"Ruan",
  "isVIP":"true"
}

GET my_index/_mapping
DELETE my_index
PUT my_index
{
  "mappings": {
    "dynamic_templates": [
            {
        "strings_as_boolean": {
          "match_mapping_type":   "string",
          "match":"is*",
          "mapping": {
            "type": "boolean"
          }
        }
      },
      {
        "strings_as_keywords": {
          "match_mapping_type":   "string",
          "mapping": {
            "type": "keyword"
          }
        }
      }
    ]
  }
}

DELETE my_index
#结合路径
PUT my_index
{
  "mappings": {
    "dynamic_templates": [
      {
        "full_name": {
          "path_match":   "name.*",
          "path_unmatch": "*.middle",
          "mapping": {
            "type":       "text",
            "copy_to":    "full_name"
          }
        }
      }
    ]
  }
}


PUT my_index/_doc/1
{
  "name": {
    "first":  "John",
    "middle": "Winston",
    "last":   "Lennon"
  }
}

GET my_index/_search?q=full_name:Lennon

---

聚合

• 聚合的分类

#按照目的地进行分桶统计
GET kibana_sample_data_flights/_search
{
	"size": 0,
	"aggs":{
		"flight_dest":{
			"terms":{
				"field":"DestCountry"
			}
		}
	}
}

#查看航班目的地的统计信息，增加平均，最高最低价格
GET kibana_sample_data_flights/_search
{
	"size": 0,
	"aggs":{
		"flight_dest":{
			"terms":{
				"field":"DestCountry"
			},
			"aggs":{
				"avg_price":{
					"avg":{
						"field":"AvgTicketPrice"
					}
				},
				"max_price":{
					"max":{
						"field":"AvgTicketPrice"
					}
				},
				"min_price":{
					"min":{
						"field":"AvgTicketPrice"
					}
				}
			}
		}
	}
}

#价格统计信息+天气信息
GET kibana_sample_data_flights/_search
{
	"size": 0,
	"aggs":{
		"flight_dest":{
			"terms":{
				"field":"DestCountry"
			},
			"aggs":{
				"stats_price":{
					"stats":{
						"field":"AvgTicketPrice"
					}
				},
				"wather":{
				  "terms": {
				    "field": "DestWeather",
				    "size": 5
				  }
				}

			}
		}
	}
}

https://www.elastic.co/guide/en/elasticsearch/reference/7.1/search-aggregations.html

---

小结

小测验1:

答案:

小测验2:

答案: