9711. Advanced Topics in Elasticsearch
Elasticsearch

Advanced Search Queries in Elastic Search.

2. Inverted Index

  • https://www.elastic.co/guide/en/elasticsearch/guide/current/inverted-index.html tokenization normalization

3. Dive to DSL

DSL: Domain-specific Language

The following queries are based on the sample employee data, created by Indexing Employee Document from ES Official Website, started from Search with Query DSL.

Search for employees who have “Smith” in their last name.

GET /megacorp/employee/_search?q=last_name:Smith

DSL Query

Same with the above one.

GET /megacorp/employee/_search

{
    "query" : {
        "match" : {
            "last_name" : "Smith"
        }
    }
}

DSL Query with Filter

GET /megacorp/employee/_search

{
    "query" : {
        "bool" : {
            "must" : {
                "match" : {
                    "last_name" : "smith"
                }
            },
            "filter" : {
                "range" : {
                    "age" : { "gt" : 30 } //range filter: older than 30
                }
            }
        }
    }
}

Full-Text Search

GET /megacorp/employee/_search
{
    "query" : {
        "match" : {
            "about" : "rock climbing"
        }
    }
}

Response:

{
   ...
   "hits": {
      "total":      2,
      "max_score":  0.16273327,
      "hits": [
         {
            ...
            "_score":         0.16273327,
            "_source": {
               "first_name":  "John",
               "last_name":   "Smith",
               "age":         25,
               "about":       "I love to go rock climbing", //exact hit
               "interests": [ "sports", "music" ]
            }
         },
         {
            ...
            "_score":         0.016878016,
            "_source": {
               "first_name":  "Jane",
               "last_name":   "Smith",
               "age":         32,
               "about":       "I like to collect rock albums", // why? rock = rock climbing?
               "interests": [ "music" ]
            }
         }
      ]
   }
}

The scores of each hit are different. Hits are sorted by score in descending order.

Match exact sequences of words or phrases. The below query only returns one hit, the first one in above sample.

GET /megacorp/employee/_search
{
    "query" : {
        "match_phrase" : {              //match exact "rock climbing"
            "about" : "rock climbing"
        }
    }
}

Highlight the Result

GET /megacorp/employee/_search
{
    "query" : {
        "match_phrase" : {
            "about" : "rock climbing"
        }
    },
    "highlight": {
        "fields" : {
            "about" : {}
        }
    }
}

Response:

{
   ...
   "hits": {
      "total":      1,
      "max_score":  0.23013961,
      "hits": [
         {
            ...
            "_score":         0.23013961,
            "_source": {
               "first_name":  "John",
               "last_name":   "Smith",
               "age":         25,
               "about":       "I love to go rock climbing",
               "interests": [ "sports", "music" ]
            },
            "highlight": {
               "about": [
                  "I love to go <em>rock</em> <em>climbing</em>"  // wrapped in <em></em> HTML tags
               ]
            }
         }
      ]
   }
}

Aggregations

find the most popular interests enjoyed by our employees:

GET /megacorp/employee/_search
{
  "aggs": {
    "all_interests": {
      "terms": { "field": "interests" }
    }
  }
}

Response:

{
   ...
   "hits": { ... },
   "aggregations": {
      "all_interests": {
         "buckets": [
            {
               "key":       "music",
               "doc_count": 2
            },
            {
               "key":       "forestry",
               "doc_count": 1
            },
            {
               "key":       "sports",
               "doc_count": 1
            }
         ]
      }
   }
}

4. Additional Chapters