Query and filter contextedit

Relevance scoresedit

By default, Elasticsearch sorts matching search results by relevance score, which measures how well each document matches a query.

The relevance score is a positive floating point number, returned in the _score meta-field of the search API. The higher the _score, the more relevant the document. While each query type can calculate relevance scores differently, score calculation also depends on whether the query clause is run in a query or filter context.

Query contextedit

In the query context, a query clause answers the question How well does this document match this query clause? Besides deciding whether or not the document matches, the query clause also calculates a relevance score in the _score meta-field.

Query context is in effect whenever a query clause is passed to a query parameter, such as the query parameter in the search API.

Filter contextedit

In a filter context, a query clause answers the question Does this document match this query clause? The answer is a simple Yes or No — no scores are calculated. Filter context is mostly used for filtering structured data, e.g.

  • Does this timestamp fall into the range 2015 to 2016?
  • Is the status field set to "published"?

Frequently used filters will be cached automatically by Elasticsearch, to speed up performance.

Filter context is in effect whenever a query clause is passed to a filter parameter, such as the filter or must_not parameters in the bool query, the filter parameter in the constant_score query, or the filter aggregation.

Example of query and filter contextsedit

Below is an example of query clauses being used in query and filter context in the search API. This query will match documents where all of the following conditions are met:

  • The title field contains the word search.
  • The content field contains the word elasticsearch.
  • The status field contains the exact word published.
  • The publish_date field contains a date from 1 Jan 2015 onwards.
GET /_search
{
  "query": { 
    "bool": { 
      "must": [
        { "match": { "title":   "Search"        }}, 
        { "match": { "content": "Elasticsearch" }}  
      ],
      "filter": [ 
        { "term":  { "status": "published" }}, 
        { "range": { "publish_date": { "gte": "2015-01-01" }}} 
      ]
    }
  }
}

The query parameter indicates query context.

The bool and two match clauses are used in query context, which means that they are used to score how well each document matches.

The filter parameter indicates filter context.

The term and range clauses are used in filter context. They will filter out documents which do not match, but they will not affect the score for matching documents.

Tip

Use query clauses in query context for conditions which should affect the score of matching documents (i.e. how well does the document match), and use all other query clauses in filter context.