[DOCS] Rewrite `fuzzy` query docs (#42078)
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James Rodewig
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<titleabbrev>Fuzzy</titleabbrev>
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++++
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The fuzzy query uses similarity based on Levenshtein edit distance.
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Returns documents that contain terms similar to the search term, as measured by
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a http://en.wikipedia.org/wiki/Levenshtein_distance[Levenshtein edit distance].
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==== String fields
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An edit distance is the number of one-character changes needed to turn one term
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into another. These changes can include:
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The `fuzzy` query generates matching terms that are within the
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maximum edit distance specified in `fuzziness` and then checks the term
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dictionary to find out which of those generated terms actually exist in the
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index. The final query uses up to `max_expansions` matching terms.
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* Changing a character (**b**ox → **f**ox)
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* Removing a character (**b**lack → lack)
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* Inserting a character (sic → sic**k**)
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* Transposing two adjacent characters (**ac**t → **ca**t)
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Here is a simple example:
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To find similar terms, the `fuzzy` query creates a set of all possible
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variations, or expansions, of the search term within a specified edit distance.
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The query then returns exact matches for each expansion.
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[[fuzzy-query-ex-request]]
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==== Example requests
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[[fuzzy-query-ex-simple]]
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===== Simple example
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[source,js]
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--------------------------------------------------
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----
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GET /_search
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{
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"query": {
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"fuzzy" : { "user" : "ki" }
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}
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}
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--------------------------------------------------
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// CONSOLE
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Or with more advanced settings:
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[source,js]
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--------------------------------------------------
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GET /_search
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{
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"query": {
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"fuzzy" : {
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"user" : {
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"value": "ki",
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"boost": 1.0,
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"fuzziness": 2,
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"prefix_length": 0,
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"max_expansions": 100
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"fuzzy": {
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"user": {
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"value": "ki"
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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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// CONSOLE
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[float]
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===== Parameters
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[[fuzzy-query-ex-advanced]]
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===== Example using advanced parameters
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[source,js]
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----
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GET /_search
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{
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"query": {
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"fuzzy": {
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"user": {
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"value": "ki",
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"fuzziness": "AUTO",
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"max_expansions": 50,
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"prefix_length": 0,
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"transpositions": true,
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"rewrite": "constant_score"
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}
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}
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}
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}
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----
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// CONSOLE
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[[fuzzy-query-top-level-params]]
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==== Top-level parameters for `fuzzy`
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`<field>`::
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(Required, object) Field you wish to search.
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[[fuzzy-query-field-params]]
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==== Parameters for `<field>`
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`value`::
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(Required, string) Term you wish to find in the provided `<field>`.
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[horizontal]
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`fuzziness`::
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(Optional, string) Maximum edit distance allowed for matching. See <<fuzziness>>
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for valid values and more information.
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The maximum edit distance. Defaults to `AUTO`. See <<fuzziness>>.
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`prefix_length`::
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The number of initial characters which will not be ``fuzzified''. This
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helps to reduce the number of terms which must be examined. Defaults
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to `0`.
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`max_expansions`::
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+
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--
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(Optional, integer) Maximum number of variations created. Defaults to `50`.
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The maximum number of terms that the `fuzzy` query will expand to.
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Defaults to `50`.
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WARNING: Avoid using a high value in the `max_expansions` parameter, especially
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if the `prefix_length` parameter value is `0`. High values in the
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`max_expansions` parameter can cause poor performance due to the high number of
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variations examined.
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--
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`prefix_length`::
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(Optional, integer) Number of beginning characters left unchanged when creating
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expansions. Defaults to `0`.
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`transpositions`::
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(Optional, boolean) Indicates whether edits include transpositions of two
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adjacent characters (ab → ba). Defaults to `true`.
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Whether fuzzy transpositions (`ab` -> `ba`) are supported.
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Default is `true`.
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WARNING: This query can be very heavy if `prefix_length` is set to `0` and if
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`max_expansions` is set to a high number. It could result in every term in the
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index being examined!
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`rewrite`::
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(Optional, string) Method used to rewrite the query. For valid values and more
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information, see the <<query-dsl-multi-term-rewrite, `rewrite` parameter>>.
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