4.1-基于词项和基于全文的搜索

2020-03-30 本文已影响0人落日彼岸

基于 Term 的查询

Term 的重要性
- Term 是表达语意的最⼩单位。搜索和利⽤统计语⾔模型进⾏⾃然语⾔处理都需要处理 Term
特点
- Term Level Query: Term Query / Range Query / Exists Query / Prefix Query /Wildcard Query
- 在 ES 中，Term 查询，对输⼊不做分词。会将输⼊作为⼀个整体，在倒排索引中查找准确的词项，并且使⽤相关度算分公式为每个包含该词项的⽂档进⾏相关度算分 – 例如“Apple Store”
- 可以通过 Constant Score 将查询转换成⼀个 Filtering，避免算分，并利⽤缓存，提⾼性

关于 Term 查询的例子

POST /products/_bulk
{ "index": { "_id": 1 }}
{ "productID" : "XHDK-A-1293-#fJ3","desc":"iPhone" }
{ "index": { "_id": 2 }}
{ "productID" : "KDKE-B-9947-#kL5","desc":"iPad" }
{ "index": { "_id": 3 }}
{ "productID" : "JODL-X-1937-#pV7","desc":"MBP" }

几个查询的结果分别是什么?
如果搜不不到，为什么?
应该如何解决

GET /products

POST /products/_search
{
  "query": {
    "term": {
      "desc": {
        //"value": "iPhone" //查不到结果
        "value":"iphone" //可以查到结果
      }
    }
  }
}

POST /products/_search
{
  "query": {
    "term": {
      "desc.keyword": {
        "value": "iPhone" //可以查到结果
        //"value":"iphone" //查不到结果
      }
    }
  }
}


POST /products/_search
{
  "query": {
    "term": {
      "productID": {
        "value": "XHDK-A-1293-#fJ3" //查不到结果
        //"value": "xhdk" //可以查到结果,根据分词分析
        //"value": "xhdk-a-1293-#fJ3" //查不到结果
      }
    }
  }
}

POST /products/_search
{
  //"explain": true,
  "query": {
    "term": {
      "productID.keyword": {
        "value": "XHDK-A-1293-#fJ3"//可以查到结果
      }
    }
  }
}

//查看分词结果
POST /_analyze
{
 "analyzer": "standard",
 "text": ["XHDK-A-1293-#fJ3"]
}

//res
{
  "tokens" : [
    {
      "token" : "xhdk",
      "start_offset" : 0,
      "end_offset" : 4,
      "type" : "<ALPHANUM>",
      "position" : 0
    },
    {
      "token" : "a",
      "start_offset" : 5,
      "end_offset" : 6,
      "type" : "<ALPHANUM>",
      "position" : 1
    },
    {
      "token" : "1293",
      "start_offset" : 7,
      "end_offset" : 11,
      "type" : "<NUM>",
      "position" : 2
    },
    {
      "token" : "fj3",
      "start_offset" : 13,
      "end_offset" : 16,
      "type" : "<ALPHANUM>",
      "position" : 3
    }
  ]
}

多字段 Mapping 和 Term查询

GET products/_mapping

//res
{
  "products" : {
    "mappings" : {
      "properties" : {
        "desc" : {
          "type" : "text",
          "fields" : {
            "keyword" : {
              "type" : "keyword",
              "ignore_above" : 256
            }
          }
        },
        "productID" : {
          "type" : "text",
          "fields" : {
            "keyword" : {
              "type" : "keyword",
              "ignore_above" : 256
            }
          }
        }
      }
    }
  }
}

使用keyword关键字进行查询,严格匹配
term查询会返回算分结果

复合查询 – Constant Score 转为 Filter

将 Query 转成 Filter，忽略 TF-IDF 计算，避免相关性算分的开销
Filter 可以有效利⽤缓存

POST /products/_search
{
  "explain": true,
  "query": {
    "constant_score": {
      "filter": {
        "term": {
          "productID.keyword": "XHDK-A-1293-#fJ3"
        }
      }
    }
  }
}

//res
{
  "took" : 8,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 1,
      "relation" : "eq"
    },
    "max_score" : 1.0,
    "hits" : [
      {
        "_shard" : "[products][0]",
        "_node" : "BsfHcVuGT8-7CROZ1odZUg",
        "_index" : "products",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 1.0,
        "_source" : {
          "productID" : "XHDK-A-1293-#fJ3",
          "desc" : "iPhone"
        },
        "_explanation" : {
          "value" : 1.0,
          "description" : "ConstantScore(productID.keyword:XHDK-A-1293-#fJ3)",
          "details" : [ ]
        }
      }
    ]
  }
}

基于全⽂的查询

基于全⽂本的查找
- Match Query / Match Phrase Query / Query String Query
特点
索引和搜索时都会进⾏分词，查询字符串先传递到⼀个合适的分词器，然后⽣成⼀个供查询的词项列表
查询时候，先会对输⼊的查询进⾏分词，然后每个词项逐个进⾏底层的查询，最终将结果进⾏合并。并为每个⽂档⽣成⼀个算分。

例如查 “Matrix reloaded”，会查到包括Matrix 或者 reload的所有结果。

Match Query Result

POST /movies/_search
{
  "profile": "true", 
  "query": {
    "match": {
      "title": {
        "query": "Matrix reload" // or
      }
    }
  }
}

//res
"hits" : [
      {
        "_index" : "movies",
        "_type" : "_doc",
        "_id" : "2571",
        "_score" : 9.095142, //返回相关的算分结果
        "_source" : {
          "genre" : [
            "Action",
            "Sci-Fi",
            "Thriller"
          ],
          "title" : "Matrix, The",
          "year" : 1999,
          "@version" : "1",
          "id" : "2571"
        }
      }
    ]

Operator

POST /movies/_search
{
  "profile": "true", 
  "query": {
    "match": {
      "title": {
        "query": "Matrix reload"
        , "operator": "and" //精准筛选
      }
    }
  }
}

//res
"profile" : {
    "shards" : [
      {
        "id" : "[QG8Co41UQGKuwzGrkvpzOA][movies][0]",
        "searches" : [
          {
            "query" : [
              {
                "type" : "BooleanQuery",
                "description" : "+title:matrix +title:reload",//精准筛选
                "time_in_nanos" : 2900408,

Minimum_should_match

POST /movies/_search
{
  "profile": "true", 
  "query": {
    "match": {
      "title": {
        "query": "Matrix reload",
        "minimum_should_match": 2
      }
    }
  }
}

//res
"profile" : {
    "shards" : [
      {
        "id" : "[BsfHcVuGT8-7CROZ1odZUg][movies][0]",
        "searches" : [
          {
            "query" : [
              {
                "type" : "BooleanQuery",
                "description" : "(title:matrix title:reload)~2",
                "time_in_nanos" : 5050509,

Match Phrase Query

POST /movies/_search
{
  "profile": "true", 
  "query": {
    "match_phrase": {
      "title": {
        "query": "Matrix reload",
        "slop": 1
      }
    }
  }
}

//res
"profile" : {
    "shards" : [
      {
        "id" : "[BsfHcVuGT8-7CROZ1odZUg][movies][0]",
        "searches" : [
          {
            "query" : [
              {
                "type" : "PhraseQuery",
                "description" : """title:"matrix reload"~1""",

Match Query 查询过程

基于全⽂本的查找
- Match Query / Match Phrase Query / Query String Query
基于全⽂本的查询的特点
- 索引和搜索时都会进⾏分词，查询字符串先传递到⼀个合适的分词器，然后⽣成⼀个供查询的词项列表
- 查询会对每个词项逐个进⾏底层的查询，再将结果进⾏合并。并为每个⽂档⽣成⼀个算分

本节知识点回顾

基于词项的查找 vs 基于全⽂的查找
通过字段 Mapping 控制字段的分词
- "Text" vs "Keyword"
通过参数控制查询的 Precision & Recall
复合查询 – Constant Score 查询
- 即便是对 Keyword 进⾏ Term 查询，同样会进⾏算分
- 可以将查询转为 Filtering，取消相关性算分的环节，以提升性能

课程demo

DELETE products
PUT products
{
  "settings": {
    "number_of_shards": 1
  }
}


POST /products/_bulk
{ "index": { "_id": 1 }}
{ "productID" : "XHDK-A-1293-#fJ3","desc":"iPhone" }
{ "index": { "_id": 2 }}
{ "productID" : "KDKE-B-9947-#kL5","desc":"iPad" }
{ "index": { "_id": 3 }}
{ "productID" : "JODL-X-1937-#pV7","desc":"MBP" }

GET /products

POST /products/_search
{
  "query": {
    "term": {
      "desc": {
        //"value": "iPhone"
        "value":"iphone"
      }
    }
  }
}

POST /products/_search
{
  "query": {
    "term": {
      "desc.keyword": {
        //"value": "iPhone"
        //"value":"iphone"
      }
    }
  }
}


POST /products/_search
{
  "query": {
    "term": {
      "productID": {
        "value": "XHDK-A-1293-#fJ3"
      }
    }
  }
}

POST /products/_search
{
  //"explain": true,
  "query": {
    "term": {
      "productID.keyword": {
        "value": "XHDK-A-1293-#fJ3"
      }
    }
  }
}




POST /products/_search
{
  "explain": true,
  "query": {
    "constant_score": {
      "filter": {
        "term": {
          "productID.keyword": "XHDK-A-1293-#fJ3"
        }
      }

    }
  }
}


#设置 position_increment_gap
DELETE groups
PUT groups
{
  "mappings": {
    "properties": {
      "names":{
        "type": "text",
        "position_increment_gap": 0
      }
    }
  }
}

GET groups/_mapping

POST groups/_doc
{
  "names": [ "John Water", "Water Smith"]
}

POST groups/_search
{
  "query": {
    "match_phrase": {
      "names": {
        "query": "Water Water",
        "slop": 100
      }
    }
  }
}


POST groups/_search
{
  "query": {
    "match_phrase": {
      "names": "Water Smith"
    }
  }
}

相关阅读

https://www.elastic.co/guide/en/elasticsearch/reference/7.1/term-level-queries.html
https://www.elastic.co/guide/en/elasticsearch/reference/7.1/full-text-queries.html

4.1-基于词项和基于全文的搜索

基于 Term 的查询

关于 Term 查询的例子

多字段 Mapping 和 Term查询

复合查询 – Constant Score 转为 Filter

基于全⽂的查询

Match Query Result

Operator

Minimum_should_match

Match Phrase Query

Match Query 查询过程

本节知识点回顾

课程demo

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