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71e734647b
In the example we show an `exists` query inside a constant score query. While this is possible, it can mislead users to think it is necessary so we should remove it.
73 lines
2.1 KiB
Plaintext
73 lines
2.1 KiB
Plaintext
[[query-dsl-exists-query]]
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=== Exists Query
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Returns documents that have at least one non-`null` value in the original field:
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[source,js]
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--------------------------------------------------
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{
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"exists" : { "field" : "user" }
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}
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--------------------------------------------------
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For instance, these documents would all match the above query:
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[source,js]
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--------------------------------------------------
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{ "user": "jane" }
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{ "user": "" } <1>
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{ "user": "-" } <2>
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{ "user": ["jane"] }
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{ "user": ["jane", null ] } <3>
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--------------------------------------------------
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<1> An empty string is a non-`null` value.
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<2> Even though the `standard` analyzer would emit zero tokens, the original field is non-`null`.
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<3> At least one non-`null` value is required.
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These documents would *not* match the above query:
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[source,js]
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--------------------------------------------------
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{ "user": null }
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{ "user": [] } <1>
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{ "user": [null] } <2>
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{ "foo": "bar" } <3>
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--------------------------------------------------
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<1> This field has no values.
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<2> At least one non-`null` value is required.
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<3> The `user` field is missing completely.
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[float]
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===== `null_value` mapping
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If the field mapping includes the <<null-value,`null_value`>> setting
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then explicit `null` values are replaced with the specified `null_value`. For
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instance, if the `user` field were mapped as follows:
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[source,js]
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--------------------------------------------------
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"user": {
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"type": "string",
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"null_value": "_null_"
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}
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--------------------------------------------------
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then explicit `null` values would be indexed as the string `_null_`, and the
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following docs would match the `exists` filter:
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[source,js]
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--------------------------------------------------
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{ "user": null }
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{ "user": [null] }
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--------------------------------------------------
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However, these docs--without explicit `null` values--would still have
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no values in the `user` field and thus would not match the `exists` filter:
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[source,js]
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--------------------------------------------------
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{ "user": [] }
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{ "foo": "bar" }
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--------------------------------------------------
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