299 lines
9.1 KiB
Plaintext
299 lines
9.1 KiB
Plaintext
[[search-field-stats]]
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== Field stats API
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experimental[]
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The field stats api allows one to find statistical properties of a field
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without executing a search, but looking up measurements that are natively
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available in the Lucene index. This can be useful to explore a dataset which
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you don't know much about. For example, this allows creating a histogram
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aggregation with meaningful intervals based on the min/max range of values.
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The field stats api by defaults executes on all indices, but can execute on
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specific indices too.
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All indices:
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[source,js]
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--------------------------------------------------
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curl -XGET "http://localhost:9200/_field_stats?fields=rating"
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--------------------------------------------------
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Specific indices:
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[source,js]
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--------------------------------------------------
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curl -XGET "http://localhost:9200/index1,index2/_field_stats?fields=rating"
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--------------------------------------------------
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Supported request options:
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[horizontal]
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`fields`:: A list of fields to compute stats for.
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`level`:: Defines if field stats should be returned on a per index level or on a
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cluster wide level. Valid values are `indices` and `cluster` (default).
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Alternatively the `fields` option can also be defined in the request body:
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[source,js]
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--------------------------------------------------
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curl -XPOST "http://localhost:9200/_field_stats?level=indices" -d '{
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"fields" : ["rating"]
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}'
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--------------------------------------------------
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This is equivalent to the previous request.
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[float]
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=== Field statistics
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The field stats api is supported on string based, number based and date based fields and can return the following statistics per field:
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[horizontal]
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`max_doc`::
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The total number of documents.
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`doc_count`::
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The number of documents that have at least one term for this field, or -1 if
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this measurement isn't available on one or more shards.
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`density`::
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The percentage of documents that have at least one value for this field. This
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is a derived statistic and is based on the `max_doc` and `doc_count`.
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`sum_doc_freq`::
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The sum of each term's document frequency in this field, or -1 if this
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measurement isn't available on one or more shards.
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Document frequency is the number of documents containing a particular term.
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`sum_total_term_freq`::
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The sum of the term frequencies of all terms in this field across all
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documents, or -1 if this measurement isn't available on one or more shards.
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Term frequency is the total number of occurrences of a term in a particular
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document and field.
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`min_value`::
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The lowest value in the field.
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`min_value_as_string`::
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The lowest value in the field represented in a displayable form. All fields,
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but string fields returns this. (since string fields, represent values already as strings)
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`max_value`::
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The highest value in the field.
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`max_value_as_string`::
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The highest value in the field represented in a displayable form. All fields,
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but string fields returns this. (since string fields, represent values already as strings)
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NOTE: Documents marked as deleted (but not yet removed by the merge process)
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still affect all the mentioned statistics.
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[float]
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=== Cluster level field statistics example
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Request:
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[source,js]
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--------------------------------------------------
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curl -XGET "http://localhost:9200/_field_stats?fields=rating,answer_count,creation_date,display_name"
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--------------------------------------------------
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Response:
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[source,js]
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--------------------------------------------------
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{
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"_shards": {
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"total": 1,
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"successful": 1,
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"failed": 0
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},
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"indices": {
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"_all": { <1>
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"fields": {
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"creation_date": {
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"max_doc": 1326564,
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"doc_count": 564633,
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"density": 42,
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"sum_doc_freq": 2258532,
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"sum_total_term_freq": -1,
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"min_value": "2008-08-01T16:37:51.513Z",
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"max_value": "2013-06-02T03:23:11.593Z"
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},
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"display_name": {
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"max_doc": 1326564,
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"doc_count": 126741,
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"density": 9,
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"sum_doc_freq": 166535,
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"sum_total_term_freq": 166616,
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"min_value": "0",
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"max_value": "정혜선"
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},
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"answer_count": {
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"max_doc": 1326564,
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"doc_count": 139885,
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"density": 10,
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"sum_doc_freq": 559540,
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"sum_total_term_freq": -1,
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"min_value": 0,
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"max_value": 160
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},
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"rating": {
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"max_doc": 1326564,
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"doc_count": 437892,
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"density": 33,
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"sum_doc_freq": 1751568,
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"sum_total_term_freq": -1,
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"min_value": -14,
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"max_value": 1277
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}
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}
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}
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}
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}
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--------------------------------------------------
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<1> The `_all` key indicates that it contains the field stats of all indices in the cluster.
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[float]
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==== Indices level field statistics example
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Request:
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[source,js]
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--------------------------------------------------
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curl -XGET "http://localhost:9200/_field_stats?fields=rating,answer_count,creation_date,display_name&level=indices"
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--------------------------------------------------
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Response:
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[source,js]
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--------------------------------------------------
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{
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"_shards": {
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"total": 1,
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"successful": 1,
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"failed": 0
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},
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"indices": {
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"stack": { <1>
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"fields": {
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"creation_date": {
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"max_doc": 1326564,
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"doc_count": 564633,
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"density": 42,
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"sum_doc_freq": 2258532,
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"sum_total_term_freq": -1,
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"min_value": "2008-08-01T16:37:51.513Z",
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"max_value": "2013-06-02T03:23:11.593Z"
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},
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"display_name": {
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"max_doc": 1326564,
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"doc_count": 126741,
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"density": 9,
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"sum_doc_freq": 166535,
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"sum_total_term_freq": 166616,
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"min_value": "0",
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"max_value": "정혜선"
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},
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"answer_count": {
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"max_doc": 1326564,
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"doc_count": 139885,
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"density": 10,
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"sum_doc_freq": 559540,
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"sum_total_term_freq": -1,
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"min_value": 0,
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"max_value": 160
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},
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"rating": {
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"max_doc": 1326564,
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"doc_count": 437892,
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"density": 33,
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"sum_doc_freq": 1751568,
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"sum_total_term_freq": -1,
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"min_value": -14,
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"max_value": 1277
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}
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}
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}
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}
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}
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--------------------------------------------------
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<1> The `stack` key means it contains all field stats for the `stack` index.
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[float]
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=== Field stats index constraints
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Field stats index constraints allows to omit all field stats for indices that don't match with the constraint. An index
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constraint can exclude indices' field stats based on the `min_value` and `max_value` statistic. This option is only
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useful if the `level` option is set to `indices`.
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For example index constraints can be useful to find out the min and max value of a particular property of your data in
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a time based scenario. The following request only returns field stats for the `answer_count` property for indices
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holding questions created in the year 2014:
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[source,js]
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--------------------------------------------------
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curl -XPOST "http://localhost:9200/_field_stats?level=indices" -d '{
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"fields" : ["answer_count"] <1>
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"index_constraints" : { <2>
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"creation_date" : { <3>
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"min_value" : { <4>
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"gte" : "2014-01-01T00:00:00.000Z"
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},
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"max_value" : {
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"lt" : "2015-01-01T00:00:00.000Z"
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}
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}
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}
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}'
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--------------------------------------------------
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<1> The fields to compute and return field stats for.
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<2> The set index constraints. Note that index constrains can be defined for fields that aren't defined in the `fields` option.
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<3> Index constraints for the field `creation_date`.
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<4> An index constraint on the `min_value` property of a field statistic.
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For a field, index constraints can be defined on the `min_value` statistic, `max_value` statistic or both.
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Each index constraint support the following comparisons:
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[horizontal]
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`gte`:: Greater-than or equal to
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`gt`:: Greater-than
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`lte`:: Less-than or equal to
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`lt`:: Less-than
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Field stats index constraints on date fields optionally accept a `format` option, used to parse the constraint's value.
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If missing, the format configured in the field's mapping is used.
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[source,js]
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--------------------------------------------------
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curl -XPOST "http://localhost:9200/_field_stats?level=indices" -d '{
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"fields" : ["answer_count"]
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"index_constraints" : {
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"creation_date" : {
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"min_value" : {
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"gte" : "2014-01-01",
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"format" : "date_optional_time" <1>
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},
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"max_value" : {
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"lt" : "2015-01-01",
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"format" : "date_optional_time"
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}
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}
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}
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}'
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--------------------------------------------------
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<1> Custom date format |