OpenSearch/docs/reference/how-to/recipes/stemming.asciidoc

[[mixing-exact-search-with-stemming]]
=== Mixing exact search with stemming

When building a search application, stemming is often a must as it is desirable
for a query on `skiing` to match documents that contain `ski` or `skis`. But
what if a user wants to search for `skiing` specifically? The typical way to do
this would be to use a <<multi-fields,multi-field>> in order to have the same
content indexed in two different ways:

[source,console]
--------------------------------------------------
PUT index
{
  "settings": {
    "analysis": {
      "analyzer": {
        "english_exact": {
          "tokenizer": "standard",
          "filter": [
            "lowercase"
          ]
        }
      }
    }
  },
  "mappings": {
    "properties": {
      "body": {
        "type": "text",
        "analyzer": "english",
        "fields": {
          "exact": {
            "type": "text",
            "analyzer": "english_exact"
          }
        }
      }
    }
  }
}

PUT index/_doc/1
{
  "body": "Ski resort"
}

PUT index/_doc/2
{
  "body": "A pair of skis"
}

POST index/_refresh
--------------------------------------------------

With such a setup, searching for `ski` on `body` would return both documents:

[source,console]
--------------------------------------------------
GET index/_search
{
  "query": {
    "simple_query_string": {
      "fields": [ "body" ],
      "query": "ski"
    }
  }
}
--------------------------------------------------
// TEST[continued]

[source,console-result]
--------------------------------------------------
{
  "took": 2,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped" : 0,
    "failed": 0
  },
  "hits": {
    "total" : {
        "value": 2,
        "relation": "eq"
    },
    "max_score": 0.18232156,
    "hits": [
      {
        "_index": "index",
        "_type": "_doc",
        "_id": "1",
        "_score": 0.18232156,
        "_source": {
          "body": "Ski resort"
        }
      },
      {
        "_index": "index",
        "_type": "_doc",
        "_id": "2",
        "_score": 0.18232156,
        "_source": {
          "body": "A pair of skis"
        }
      }
    ]
  }
}
--------------------------------------------------
// TESTRESPONSE[s/"took": 2,/"took": "$body.took",/]

On the other hand, searching for `ski` on `body.exact` would only return
document `1` since the analysis chain of `body.exact` does not perform
stemming.

[source,console]
--------------------------------------------------
GET index/_search
{
  "query": {
    "simple_query_string": {
      "fields": [ "body.exact" ],
      "query": "ski"
    }
  }
}
--------------------------------------------------
// TEST[continued]

[source,console-result]
--------------------------------------------------
{
  "took": 1,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped" : 0,
    "failed": 0
  },
  "hits": {
    "total" : {
        "value": 1,
        "relation": "eq"
    },
    "max_score": 0.8025915,
    "hits": [
      {
        "_index": "index",
        "_type": "_doc",
        "_id": "1",
        "_score": 0.8025915,
        "_source": {
          "body": "Ski resort"
        }
      }
    ]
  }
}
--------------------------------------------------
// TESTRESPONSE[s/"took": 1,/"took": "$body.took",/]

This is not something that is easy to expose to end users, as we would need to
have a way to figure out whether they are looking for an exact match or not and
redirect to the appropriate field accordingly. Also what to do if only parts of
the query need to be matched exactly while other parts should still take
stemming into account?

Fortunately, the `query_string` and `simple_query_string` queries have a feature
that solves this exact problem: `quote_field_suffix`. This tells Elasticsearch
that the words that appear in between quotes are to be redirected to a different
field, see below:

[source,console]
--------------------------------------------------
GET index/_search
{
  "query": {
    "simple_query_string": {
      "fields": [ "body" ],
      "quote_field_suffix": ".exact",
      "query": "\"ski\""
    }
  }
}
--------------------------------------------------
// TEST[continued]

[source,console-result]
--------------------------------------------------
{
  "took": 2,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped" : 0,
    "failed": 0
  },
  "hits": {
    "total" : {
        "value": 1,
        "relation": "eq"
    },
    "max_score": 0.8025915,
    "hits": [
      {
        "_index": "index",
        "_type": "_doc",
        "_id": "1",
        "_score": 0.8025915,
        "_source": {
          "body": "Ski resort"
        }
      }
    ]
  }
}
--------------------------------------------------
// TESTRESPONSE[s/"took": 2,/"took": "$body.took",/]

In the above case, since `ski` was in-between quotes, it was searched on the
`body.exact` field due to the `quote_field_suffix` parameter, so only document
`1` matched. This allows users to mix exact search with stemmed search as they
like.

NOTE: If the choice of field passed in `quote_field_suffix` does not exist 
the search will fall back to using the default field for the query string.