20_How_match_uses_bool.asciidoc

How match Uses bool

By now, you have probably realized that multiword match queries simply wrap the generated term queries in a bool query. With the default or operator, each term query is added as a should clause, so at least one clause must match. These two queries are equivalent:

{
    "match": { "title": "brown fox"}
}

{
  "bool": {
    "should": [
      { "term": { "title": "brown" }},
      { "term": { "title": "fox"   }}
    ]
  }
}

With the and operator, all the term queries are added as must clauses, so all clauses must match. These two queries are equivalent:

{
    "match": {
        "title": {
            "query":    "brown fox",
            "operator": "and"
        }
    }
}

{
  "bool": {
    "must": [
      { "term": { "title": "brown" }},
      { "term": { "title": "fox"   }}
    ]
  }
}

And if the minimum_should_match parameter is specified, it is passed directly through to the bool query, making these two queries equivalent:

{
    "match": {
        "title": {
            "query":                "quick brown fox",
            "minimum_should_match": "75%"
        }
    }
}

{
  "bool": {
    "should": [
      { "term": { "title": "brown" }},
      { "term": { "title": "fox"   }},
      { "term": { "title": "quick" }}
    ],
    "minimum_should_match": 2 (1)
  }
}

1. Because there are only three clauses, the minimum_should_match value of 75% in the match query is rounded down to 2. At least two out of the three should clauses must match.

Of course, we would normally write these types of queries by using the match query, but understanding how the match query works internally lets you take control of the process when you need to. Some things can’t be done with a single match query, such as give more weight to some query terms than to others. We will look at an example of this in the next section.