[[mapping-id-field]] === `_id` field Each document indexed is associated with a <> (see <>) and an <>. The `_id` field is not indexed as its value can be derived automatically from the <> field. The value of the `_id` field is accessible in certain queries (`term`, `terms`, `match`, `query_string`, `simple_query_string`) and scripts, but _not_ in aggregations or when sorting, where the <> field should be used instead: [source,js] -------------------------- # Example documents PUT my_index/my_type/1 { "text": "Document with ID 1" } PUT my_index/my_type/2 { "text": "Document with ID 2" } GET my_index/_search { "query": { "terms": { "_id": [ "1", "2" ] <1> } }, "script_fields": { "UID": { "script": "doc['_id']" <2> } } } -------------------------- // CONSOLE <1> Querying on the `_id` field (also see the <>) <2> Accessing the `_id` field in scripts (inline scripts must be <> for this example to work)