查詢1

POST /bank/_search
{
  "query": {
    "bool": {
      "must": {
       "term": {
         "firstname" : "Amber"
       }
      }
    }
  }
}

查詢1執(zhí)行得到結(jié)果1，找不到匹配結(jié)果

{
  "took" : 0,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 0,
      "relation" : "eq"
    },
    "max_score" : null,
    "hits" : [ ]
  }
}

查詢2

POST /bank/_search
{
  "query": {
    "bool": {
      "must": {
       "term": {
         "firstname" : "amber"
       }
      }
    }
  }
}

查詢3

POST /bank/_search
{
  "query": {
    "bool": {
      "must": {
       "term": {
         "firstname.keyword" : "Amber"
       }
      }
    }
  }
}

查詢2和查詢3執(zhí)行得到結(jié)果2

{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 6.5032897,
    "hits" : [
      {
        "_index" : "bank",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 6.5032897,
        "_source" : {
          "account_number" : 1,
          "balance" : 39225,
          "firstname" : "Amber",
          "lastname" : "Duke",
          "age" : 32,
          "gender" : "M",
          "address" : "880 Holmes Lane",
          "employer" : "Pyrami",
          "email" : "amberduke@pyrami.com",
          "city" : "Brogan",
          "state" : "IL"
        }
      }
    ]
  }
}

查詢1找不到匹配結(jié)果，而查詢2和查詢3可以得到結(jié)果2，用下面的查詢結(jié)果分析原因
查詢分詞結(jié)果：

Get /bank/_analyze
{
  "field":"firstname",
  "text":"Amber nihao  wohao"
}

分詞的結(jié)果：

{
  "tokens" : [
    {
      "token" : "amber",
      "start_offset" : 0,
      "end_offset" : 5,
      "type" : "<ALPHANUM>",
      "position" : 0
    },
    {
      "token" : "nihao",
      "start_offset" : 6,
      "end_offset" : 11,
      "type" : "<ALPHANUM>",
      "position" : 1
    },
    {
      "token" : "wohao",
      "start_offset" : 13,
      "end_offset" : 18,
      "type" : "<ALPHANUM>",
      "position" : 2
    }
  ]
}

通過分詞結(jié)果，可以看出，含有大寫字母的Amber分詞后，變成了amber，這也就是查詢2可以匹配結(jié)果，而查詢1匹配不到結(jié)果的原因。
最根本原因可以參考：https://segmentfault.com/q/1010000017312707