[[mapping-index-field]] === `_index` field When performing queries across multiple indexes, it is sometimes desirable to add query clauses that are associated with documents of only certain indexes. The `_index` field allows matching on the index a document was indexed into. Its value is accessible in `term`, or `terms` queries, aggregations, scripts, and when sorting: NOTE: The `_index` is exposed as a virtual field -- it is not added to the Lucene index as a real field. This means that you can use the `_index` field in a `term` or `terms` query (or any query that is rewritten to a `term` query, such as the `match`, `query_string` or `simple_query_string` query), but it does not support `prefix`, `wildcard`, `regexp`, or `fuzzy` queries. [source,js] -------------------------- # Example documents PUT index_1/my_type/1 { "text": "Document in index 1" } PUT index_2/my_type/2 { "text": "Document in index 2" } GET index_1,index_2/_search { "query": { "terms": { "_index": ["index_1", "index_2"] <1> } }, "aggs": { "indices": { "terms": { "field": "_index", <2> "size": 10 } } }, "sort": [ { "_index": { <3> "order": "asc" } } ], "script_fields": { "index_name": { "script": "doc['_index']" <4> } } } -------------------------- // CONSOLE <1> Querying on the `_index` field <2> Aggregating on the `_index` field <3> Sorting on the `_index` field <4> Accessing the `_index` field in scripts (inline scripts must be <> for this example to work)