Elasticsearch Boolean Clauses The four boolean clauses used for bool queries are filter, must, must _not, and should. Filter – Filter is used to par down the dataset; a document will either fit into a filter or be excluded by it.
Well, when a bool query has only should clauses, at least one of them must match. However, when that bool query also has a must clause, the should clauses instead now act as a boost factor, meaning none of them have to match but if they do, the relevancy score for that document will be boosted and thus appear higher in the results.
You can use the minimum_should_match parameter to specify the number or percentage of should clauses returned documents must match. If the bool query includes at least one should clause and no must or filter clauses, the default value is 1 .
This of course begs the question “What is a Boolean query in Elasticsearch?”
Boolean queries, or bool queries, find or match documents by using boolean clauses. For the vast majority of cases, the filtering clause will be used because it can be cached for faster search times. In this article we will describe how a boolean query is written and work through several example Elasticsearch bool queries.
What does must mean in Elasticsearch?
Must – Must is similar to the “and” operator used when making a Google search. Using must tells Elasticsearch that document matches need to include all of the queries that fall under the must clause. If you have more than one query, then all of those queries need to match.
What is constant_score in Elasticsearch?
The constant_score query assigns a score of 1.0 to all documents matched by the filter. Each query accepts a _name in its top level definition. You can use named queries to track which queries matched returned documents. If named queries are used, the response includes a matched_queries property for each hit. What is Elasticsearch?
Elasticsearch ascribes scores to matches that rank the matched documents by their relevance to the search parameters. All scores are represented by a floating number greater than zero, and the greater the score the better matched it is to the search query.
How do you score must match in Bool query?
The bool query takes a more-matches-is-better approach, so the score from each matching must or should clause will be added together to provide the final _score for each document. You can use the minimum_should_match parameter to specify the number or percentage of should clauses returned documents must match.