Use runtime fieldsedit

Use the runtime_mappings parameter to extract and create runtime fields, or columns, from existing ones during a search.

The following search creates a release_day_of_week runtime field from release_date and returns it in the response.

POST _sql?format=txt
{
  "runtime_mappings": {
    "release_day_of_week": {
      "type": "keyword",
      "script": """
        emit(doc['release_date'].value.dayOfWeekEnum.toString())
      """
    }
  },
  "query": """
    SELECT * FROM library WHERE page_count > 300 AND author = 'Frank Herbert'
  """
}

The API returns:

    author     |     name      |  page_count   |      release_date      |release_day_of_week
---------------+---------------+---------------+------------------------+-------------------
Frank Herbert  |Dune           |604            |1965-06-01T00:00:00.000Z|TUESDAY