Phrase boosting in multi-match query

Elastic Stack Elasticsearch
1

How can I compose a multi-match phrase query that also boosts one of the phrases? I can write a multi-match query using multiple phrases, and I can write a multi-match query that boosts single keywords, but I'd like to do both simultaneously.

Boosting one keyword

I can boost one keyword in a multi-match query.

GET _search
{
  "query": {
    "multi_match": {
      "query":  "quick^2 brown fox",
      "fields": [ "title", "summary" ] 
    }
  }
}

Accept multiple phrases

I can look for multiple phrases in a single multi-match clause.

GET _search
{
  "query": {
    "multi_match": {
      "query":  [ "quick fox", "brown fox" ],
      "fields": [ "title", "summary" ] 
    }
  }
}

The question remains

How can I do both of the above in one clause?

2

Well, the answer is that you can't. But it's because the multi_match query doesn't accept multiple queries. It just looks like it does because you are (likely) on an older version of ES that incorrectly accepts, and then ignores, the second query. On newer versions of ES you'll get an exception:

{
   "error": {
      "root_cause": [
         {
            "type": "parsing_exception",
            "reason": "[multi_match] unknown token [START_ARRAY] after [query]",
            "line": 4,
            "col": 21
         }
      ],
      "type": "parsing_exception",
      "reason": "[multi_match] unknown token [START_ARRAY] after [query]",
      "line": 4,
      "col": 21
   },
   "status": 400
}

If you need multiple phrases against multiple fields, you'll have to do a boolean combination with one phrase per multi_match. You can then boost each of them individually. Also note, you'll need to specify "type": "phrase" to turn it into a phrase match. Something like this:

{
   "query": {
      "bool": {
         "should": [
            {
               "multi_match": {
                  "query": ["quick fox"],
                  "fields": ["title","summary"],
                  "boost": 2
               }
            },
            {
               "multi_match": {
                  "query": ["brown fox"],
                  "fields": ["title","summary"],
                  "boost": 1
               }
            }
         ]
      }
   }
}