Hello, Upon indexing, elastic allocates a unique _id <https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-id-field.html> for each document (unless specified by the user). Currently when mapping between elastic result and calcite return type we query only _source or fields attributes. _id is not part those but exposed at higher level in query response (see SearchHit <https://www.elastic.co/guide/en/elasticsearch/reference/6.1/_the_search_api.html> ). Currently _MAP['foo'] becomes _source.get('foo') (or fields.get('foo')). Do you think we should make _MAP['_id'] available implicitly ? I have a couple of use-cases where one needs to know document ID. Please note this makes sense only for non-aggregate queries. Regards, Andrei.