OpenSearch/docs/reference/query-dsl/span-field-masking-query.asciidoc

[[query-dsl-span-field-masking-query]]
=== Span field masking query
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<titleabbrev>Span field masking</titleabbrev>
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Wrapper to allow span queries to participate in composite single-field span queries by 'lying' about their search field. The span field masking query maps to Lucene's `SpanFieldMaskingQuery`

This can be used to support queries like `span-near` or `span-or` across different fields, which is not ordinarily permitted.

Span field masking query is invaluable in conjunction with *multi-fields* when same content is indexed with multiple analyzers. For instance we could index a field with the standard analyzer which breaks text up into words, and again with the english analyzer which stems words into their root form.

Example:

[source,console]
--------------------------------------------------
GET /_search
{
  "query": {
    "span_near": {
      "clauses": [
        {
          "span_term": {
            "text": "quick brown"
          }
        },
        {
          "field_masking_span": {
            "query": {
              "span_term": {
                "text.stems": "fox"
              }
            },
            "field": "text"
          }
        }
      ],
      "slop": 5,
      "in_order": false
    }
  }
}
--------------------------------------------------

Note: as span field masking query returns the masked field, scoring will be done using the norms of the field name supplied. This may lead to unexpected scoring behaviour.