elasticsearch/docs/reference/query-languages/esql/esql-metadata-fields.md

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Metadata fields	https://www.elastic.co/guide/en/elasticsearch/reference/current/esql-metadata-fields.html

{{esql}} metadata fields [esql-metadata-fields]

{{esql}} can access metadata fields.

To access these fields, use the METADATA directive with the FROM source command. For example:

FROM index METADATA _index, _id

Available metadata fields

The following metadata fields are available in {{esql}}:

Metadata field	Type	Description
_id	keyword	Unique document ID.
_ignored	keyword	Names every field in a document that was ignored when the document was indexed.
_index	keyword	Index name.
_index_mode	keyword	Index mode. For example: standard, lookup, or logsdb.
_score	float	Query relevance score (when enabled). Scores are updated when using full text search functions.
_source	Special _source type	Original JSON document body passed at index time (or a reconstructed version if synthetic _source is enabled).
_version	long	Document version number

Usage and limitations

• Metadata fields are only available when the data source is an index
• The _source type is not supported by functions
• Only the FROM command supports the METADATA directive
• Once enabled, metadata fields work like regular index fields

Examples

Basic metadata usage

Once enabled, metadata fields are available to subsequent processing commands, just like other index fields:

FROM ul_logs, apps METADATA _index, _version
| WHERE id IN (13, 14) AND _version == 1
| EVAL key = CONCAT(_index, "_", TO_STR(id))
| SORT id, _index
| KEEP id, _index, _version, key

id:long	_index:keyword	_version:long	key:keyword
13	apps	1	apps_13
13	ul_logs	1	ul_logs_13
14	apps	1	apps_14
14	ul_logs	1	ul_logs_14

Metadata fields and aggregations

Similar to index fields, once an aggregation is performed, a metadata field will no longer be accessible to subsequent commands, unless used as a grouping field:

FROM employees METADATA _index, _id
| STATS max = MAX(emp_no) BY _index

max:integer	_index:keyword
10100	employees

Sort results by search score

FROM products METADATA _score
| WHERE MATCH(description, "wireless headphones")
| SORT _score DESC
| KEEP name, description, _score

:::{tip} Refer to {{esql}} for search for more information on relevance scoring and how to use _score in your queries. :::