How elasticsearch decides must and filter terms in same query?-CodePudding

The following query includes must and filter contexts in same query.

GET /_search
{
  "query": { 
    "bool": { 
      "must": [
        { "match": { "title":   "Search"        }},
        { "match": { "content": "Elasticsearch" }}
      ],
      "filter": [ 
        { "term":  { "status": "published" }}
      ]
    }
  }
}

if there are some documents that matches with must logic but not matches with filer logic, so I am getting no result? Is filter most important? How works this query order? First must logic and then filter logic?

CodePudding user response：

Here it will match all the conditions of MUST & FILTERS. You can see MUST & FILTER something like AND query. So the query will go like title="search" AND content="Elasticsearch" AND status="published".

The only difference is MUST contributes to scoring where FILTER is not.

So if you hit same query like below,

GET /_search
{
  "query": { 
    "bool": { 
      "must": [
        { "match": { "title":   "Search"        }},
        { "match": { "content": "Elasticsearch" }},
        { "term":  { "status": "published" }}
      ]
    }
  }
}

You will see the different _score value with same result.

So simple is if you want to ignore scoring just use filter.

Mostly filters are use with conditions like <,>,<=,>=,= or where you don't want score.

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

Check more in doc