二十、Elasticsearch混合使用match和match_

1、什么是召回率？

比如你搜索一个java spark，总共有100个doc，能返回多少个doc作为结果，就是召回率，recall

2、什么是精准度？

比如你搜索一个java spark，能不能尽可能让包含java spark或者是java和spark离的很近的doc排在最前面，precision直接用match_phrase短语搜索，会导致必须所有term都在doc field中出现，而且距离在slop限定范围内才能匹配上。

match_phrase,proximity match要求doc必须包含所有的term，才能作为结果返回；如果某一个doc可能就是有某个term没有包含，那么就无法作为结果返回。

比如：
java spark --》 hello world java ： 就无法匹配到
java spark --》 hello world，java spark ： 可以匹配到

3、疑问
近似匹配的时候，召回率比较低，精准度太高了，但是有时我们希望的是匹配到几个term中的部分，就可以作为结果出来，这样可以提高召回率，同时我们也希望用上match_phrase根据距离提升分数的功能，让几个term距离越近分数就越高，越优先返回。

就是优先满足召回率。比如
java spark --》 包含java的返回，包含spark的也返回，包含 java和spark的也返回，同时兼顾精准度，就是包含java和spark，同时java和spark距离越近的doc排最前面。

4、解决疑问
可以用bool组合match query和match_phrase query一起，来实现上述效果。

match提高召回率，带java和带spark的都要返回。
match_phrase提高精准度，保证同时带java和spark的排在最前面。

效果1：直接用bool match query

GET /forum/article/_search 
{
  "query": {
    "bool": {
      "must": [
        {
          "match": {
            "content": "java spark"
          }
        }
      ]
    }
  }
}

结果

{
  "took": 54,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "failed": 0
  },
  "hits": {
    "total": 2,
    "max_score": 0.68640786,
    "hits": [
      {
        "_index": "forum",
        "_type": "article",
        "_id": "2",
        "_score": 0.68640786,
        "_source": {
          "articleID": "KDKE-B-9947-#kL5",
          "userID": 1,
          "hidden": false,
          "postDate": "2017-01-02",
          "tag": [
            "java"
          ],
          "tag_cnt": 1,
          "view_cnt": 50,
          "title": "this is java blog",
          "content": "i think java is the best programming language",
          "sub_title": "learned a lot of course",
          "author_first_name": "Smith",
          "author_last_name": "Williams",
          "new_author_last_name": "Williams",
          "new_author_first_name": "Smith"
        }
      },
      {
        "_index": "forum",
        "_type": "article",
        "_id": "5",
        "_score": 0.68324494,
        "_source": {
          "articleID": "DHJK-B-1395-#Ky5",
          "userID": 3,
          "hidden": false,
          "postDate": "2017-03-01",
          "tag": [
            "elasticsearch"
          ],
          "tag_cnt": 1,
          "view_cnt": 10,
          "title": "this is spark blog",
          "content": "spark is best big data solution based on scala ,an programming language similar to java spark",
          "sub_title": "haha, hello world",
          "author_first_name": "Tonny",
          "author_last_name": "Peter Smith",
          "new_author_last_name": "Peter Smith",
          "new_author_first_name": "Tonny"
        }
      }
    ]
  }
}

结果发现单独包含java和spark的也被返回了，而且单独包含java的却排到了第一位，既包含java又包含spark的却排到了最后。

效果2：直接用match_phrase

GET /forum/article/_search 
{
  "query": {
    "match_phrase": {
      "content": {
        "query": "java spark",
        "slop" : 50
      }
    }
  }
}

结果：

{
  "took": 3,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "failed": 0
  },
  "hits": {
    "total": 1,
    "max_score": 0.5753642,
    "hits": [
      {
        "_index": "forum",
        "_type": "article",
        "_id": "5",
        "_score": 0.5753642,
        "_source": {
          "articleID": "DHJK-B-1395-#Ky5",
          "userID": 3,
          "hidden": false,
          "postDate": "2017-03-01",
          "tag": [
            "elasticsearch"
          ],
          "tag_cnt": 1,
          "view_cnt": 10,
          "title": "this is spark blog",
          "content": "spark is best big data solution based on scala ,an programming language similar to java spark",
          "sub_title": "haha, hello world",
          "author_first_name": "Tonny",
          "author_last_name": "Peter Smith",
          "new_author_last_name": "Peter Smith",
          "new_author_first_name": "Tonny"
        }
      }
    ]
  }
}

结果发现只返回了既包含java又包含spark的数据，召回率降低了。

最终效果：我们将两个结果合并，既用bool match query又用match_phrase

GET /forum/article/_search 
{
  "query": {
    "bool": {
      "must": [
        {
          "match": {
            "content": "java spark"
          }
        }
      ],
      "should": [
        {
          "match_phrase": {
            "content": {
              "query": "java spark",
              "slop" : 50
            }
          }
        }
      ]
    }
  }
}

结果:

{
  "took": 4,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "failed": 0
  },
  "hits": {
    "total": 2,
    "max_score": 1.258609,
    "hits": [
      {
        "_index": "forum",
        "_type": "article",
        "_id": "5",
        "_score": 1.258609,
        "_source": {
          "articleID": "DHJK-B-1395-#Ky5",
          "userID": 3,
          "hidden": false,
          "postDate": "2017-03-01",
          "tag": [
            "elasticsearch"
          ],
          "tag_cnt": 1,
          "view_cnt": 10,
          "title": "this is spark blog",
          "content": "spark is best big data solution based on scala ,an programming language similar to java spark",
          "sub_title": "haha, hello world",
          "author_first_name": "Tonny",
          "author_last_name": "Peter Smith",
          "new_author_last_name": "Peter Smith",
          "new_author_first_name": "Tonny"
        }
      },
      {
        "_index": "forum",
        "_type": "article",
        "_id": "2",
        "_score": 0.68640786,
        "_source": {
          "articleID": "KDKE-B-9947-#kL5",
          "userID": 1,
          "hidden": false,
          "postDate": "2017-01-02",
          "tag": [
            "java"
          ],
          "tag_cnt": 1,
          "view_cnt": 50,
          "title": "this is java blog",
          "content": "i think java is the best programming language",
          "sub_title": "learned a lot of course",
          "author_first_name": "Smith",
          "author_last_name": "Williams",
          "new_author_last_name": "Williams",
          "new_author_first_name": "Smith"
        }
      }
    ]
  }
}

结果发现非常完美，两个都包含的排到了第一位，并且分数远高于第二个。而且召回率也很高

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