## elasticsearch-查询

elasticsearch-查询

mapping:

PUT movies
{
  "mappings": {
    "properties": {
      "title": {
        "type": "text",
        "fields": {
          "original": {
            "type": "keyword"
          }
        }
      },
      "synopsis": {
        "type": "text"
      },
      "actors": {
        "type": "text"
      },
      "director": {
        "type": "text"
      },
      "rating": {
        "type": "half_float"
      },
      "release_date": {
        "type": "date",
        "format": "dd-MM-yyyy"
      },
      "certificate": {
        "type": "keyword"
      },
      "genre": {
        "type": "text"
      }
    }
  }
}

Term query

精确查询，对于查询字段不会使用分词器拆分

GET /movies/_search
{
  "query": {
    "term": {
      "title": {
        "value": "The Shawshank Redemption" //查询字段不分词
      }
    }
  }
}

当使用 term查询，虽然文档中有这条数据，但是使用这个查询却返回为空

因为索引中title字段的类型是text, text 类型在写入的过程中就被分词，并且存储在索引中。 term queries are not suitable when working with text field， they are intended to be used on non text fields like keywords, numericals, and dates.

换成下面就可以查询到

GET /movies/_search
{
  "query": {
    "term": {
      "title.keyword": "The Shawshank Redemption"
    }
  }
}

Terms query

多个 term 查询

GET /movies/_search
{
  "query": {
    "terms": {
      "title.keyword": [
        "The Shawshank Redemption",
        "The Godfather"
      ]
    }
  }
}

Id query

GET /movies/_search
{
  "query": {
    "ids": {
      "values": [1,2,3]
    }
  }
}

Exists query

查询索引中是字段field是否存在

GET /movies/_search
{
  "query": {
    "exists": {
      "field": "title"
    }
  }
}

Range query

GET /movies/_search
{
  "query": {
    "range": {
      "rating": {
        "gte": 9,
        "lte": 20
      }
    }
  }
}

Wildcard queries

GET /movies/_search
{
  "query": {
    "wildcard": {
      "title": {
        "value": "god*"
      }
    }
  }
}

字符	描述
* (asterisk)	匹配一个或多个
? (question mark)	匹配单个

Expensive queries

wildcard，range, prefix, fuzzy, regex, and join queries are expensive query

//关闭 昂贵查询
PUT _cluster/settings 
{ 
 "transient": { 
 "search.allow_expensive_queries": "false" 
 } 
}
//关闭之后，再使用这些查询，会报错
"reason" : "[wildcard] queries cannot be executed when 'search.allow_expensive_queries' is set to false."

Prefix queries

GET /movies/_search  //查询成功
{
  "query": {
    "prefix": {
      "title.original": {
        "value": "Th"
      }
    }
  },
  "highlight": {
    "fields": {
      "title.original": {}
    }
  }
}

注意，title.original 是 keyword 类型， 如果 换成 title 为text 类型时， prefix 会查询不到

Fuzzy queries

当我们记不清 是 rama还是 dama时，就可以使用 Fuzzy query, 可以为我们纠错，使用 fuzziness 纠错 offset

GET /movies/_search
{
  "query": {
    "fuzzy": {
      "genre": {
        "value": "rama",
        "fuzziness": 1  // 这个值从左边开始计算
      }
    }
  }
}

//结果返回 dama
{
  "took": 2,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 20,
      "relation": "eq"
    },
    "max_score": 0.23582748,
    "hits": [
      {
        "_index": "movies",
        "_id": "1",
        "_score": 0.23582748,
        "_source": {
          "genre": "Drama "
        }
      }
    ]
  }
}