- Elasticsearch Guide: other versions:
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- Release Notes
- 5.0.2 Release Notes
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- 5.0.0-alpha1 Release Notes (Changes previously released in 2.x)
WARNING: Version 5.0 of Elasticsearch has passed its EOL date.
This documentation is no longer being maintained and may be removed. If you are running this version, we strongly advise you to upgrade. For the latest information, see the current release documentation.
_all field
edit_all
field
editThe _all
field is a special catch-all field which concatenates the values
of all of the other fields into one big string, using space as a delimiter, which is then
analyzed and indexed, but not stored. This means that it can be
searched, but not retrieved.
The _all
field allows you to search for values in documents without knowing
which field contains the value. This makes it a useful option when getting
started with a new dataset. For instance:
PUT my_index/user/1 { "first_name": "John", "last_name": "Smith", "date_of_birth": "1970-10-24" } GET my_index/_search { "query": { "match": { "_all": "john smith 1970" } } }
All values treated as strings
The date_of_birth
field in the above example is recognised as a date
field
and so will index a single term representing 1970-10-24 00:00:00 UTC
. The
_all
field, however, treats all values as strings, so the date value is
indexed as the three string terms: "1970"
, "24"
, "10"
.
It is important to note that the _all
field combines the original values
from each field as a string. It does not combine the terms from each field.
The _all
field is just a text
field, and accepts the same
parameters that other string fields accept, including analyzer
,
term_vectors
, index_options
, and store
.
The _all
field can be useful, especially when exploring new data using
simple filtering. However, by concatenating field values into one big string,
the _all
field loses the distinction between short fields (more relevant)
and long fields (less relevant). For use cases where search relevance is
important, it is better to query individual fields specifically.
The _all
field is not free: it requires extra CPU cycles and uses more disk
space. If not needed, it can be completely disabled or
customised on a per-field basis.
Using the _all
field in queries
editThe query_string
and
simple_query_string
queries query
the _all
field by default, unless another field is specified:
GET _search { "query": { "query_string": { "query": "john smith 1970" } } }
The same goes for the ?q=
parameter in URI search
requests (which is rewritten to a query_string
query internally):
GET _search?q=john+smith+1970
Other queries, such as the match
and
term
queries require you to specify
the _all
field explicitly, as per the
first example.
Disabling the _all
field
editThe _all
field can be completely disabled per-type by setting enabled
to
false
:
PUT my_index { "mappings": { "type_1": { "properties": {...} }, "type_2": { "_all": { "enabled": false }, "properties": {...} } } }
If the _all
field is disabled, then URI search requests and the
query_string
and simple_query_string
queries will not be able to use it
for queries (see Using the _all
field in queries). You can configure them to use a
different field with the index.query.default_field
setting:
Excluding fields from _all
editIndividual fields can be included or excluded from the _all
field with the
include_in_all
setting.
Index boosting and the _all
field
editIndividual fields can be boosted at index time, with the boost
parameter. The _all
field takes these boosts into account:
PUT myindex { "mappings": { "mytype": { "properties": { "title": { "type": "text", "boost": 2 }, "content": { "type": "text" } } } } }
When querying the |
Using index-time boosting with the _all
field has a significant
impact on query performance. Usually the better solution is to query fields
individually, with optional query time boosting.
Custom _all
fields
editWhile there is only a single _all
field per index, the copy_to
parameter allows the creation of multiple custom _all
fields. For
instance, first_name
and last_name
fields can be combined together into
the full_name
field:
PUT myindex { "mappings": { "mytype": { "properties": { "first_name": { "type": "text", "copy_to": "full_name" }, "last_name": { "type": "text", "copy_to": "full_name" }, "full_name": { "type": "text" } } } } } PUT myindex/mytype/1 { "first_name": "John", "last_name": "Smith" } GET myindex/_search { "query": { "match": { "full_name": "John Smith" } } }
Highlighting and the _all
field
editA field can only be used for highlighting if
the original string value is available, either from the
_source
field or as a stored field.
The _all
field is not present in the _source
field and it is not stored by
default, and so cannot be highlighted. There are two options. Either
store the _all
field or highlight the
original fields.
Store the _all
field
editIf store
is set to true
, then the original field value is retrievable and
can be highlighted:
PUT myindex { "mappings": { "mytype": { "_all": { "store": true } } } } PUT myindex/mytype/1 { "first_name": "John", "last_name": "Smith" } GET _search { "query": { "match": { "_all": "John Smith" } }, "highlight": { "fields": { "_all": {} } } }
Of course, storing the _all
field will use significantly more disk space
and, because it is a combination of other fields, it may result in odd
highlighting results.
The _all
field also accepts the term_vector
and index_options
parameters, allowing the use of the fast vector highlighter and the postings
highlighter.
Highlight original fields
editYou can query the _all
field, but use the original fields for highlighting as follows:
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