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db.collection.distinct()

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Definition定义

db.collection.distinct(field, query, options)
Important

mongosh Method方法

This page documents a mongosh method. 本页记录了一个mongosh方法。This is not the documentation for database commands or language-specific drivers, such as Node.js.这不是数据库命令或特定语言驱动程序（如Node.js）的文档。

For the database command, see the distinct command.有关数据库命令，请参阅distinct命令。

For MongoDB API drivers, refer to the language-specific MongoDB driver documentation.有关MongoDB API驱动程序，请参阅特定语言的MongoDB驱动程序文档。

For the legacy mongo shell documentation, refer to the documentation for the corresponding MongoDB Server release:对于遗留的mongoshell文档，请参阅相应MongoDB Server版本的文档：

mongo shell v4.4

Finds the distinct values for a specified field across a single collection or view and returns the results in an array.在单个集合或视图中查找指定字段的不同值，并以数组形式返回结果。

This method takes the following parameters:此方法采用以下参数：

Parameter参数Type类型Description描述
fieldstringThe field for which to return distinct values.要为其返回不同值的字段。
querydocumentA query that specifies the documents from which to retrieve the distinct values.指定要从中检索不同值的文档的查询。
optionsdocumentOptional.可选的。A document that specifies the options. 指定选项的文档。See Options.请参见选项。
Note

Results must not be larger than the maximum BSON size. 结果不得大于最大BSON大小。If your results exceed the maximum BSON size, use the aggregation pipeline to retrieve distinct values using the $group operator, as described in Retrieve Distinct Values with the Aggregation Pipeline.如果结果超过最大BSON大小，请使用聚合管道使用$group运算符检索不同值，如使用聚合管道检索不同值中所述。

The following diagram shows an example db.collection.distinct() call.下图显示了db.collection.distinct()调用的示例。

Diagram of the annotated distinct operation.

Options选项

{ collation: <document> }
Field字段Type类型Description描述
collationdocumentOptional.可选的。
Specifies the collation to use for the operation.指定要用于操作的排序规则。
Collation排序规则 allows users to specify language-specific rules for string comparison, such as rules for lettercase and accent marks.允许用户为字符串比较指定特定于语言的规则，例如字母大小写和重音标记的规则。
The collation option has the following syntax:排序规则选项具有以下语法： 
collation: {
   locale: <string>,
   caseLevel: <boolean>,
   caseFirst: <string>,
   strength: <int>,
   numericOrdering: <boolean>,
   alternate: <string>,
   maxVariable: <string>,
   backwards: <boolean>
}
When specifying collation, the locale field is mandatory; all other collation fields are optional. For descriptions of the fields, see Collation Document.指定排序规则时，locale字段是必需的；所有其他排序规则字段都是可选的。有关字段的说明，请参阅排序规则文档。
If the collation is unspecified but the collection has a default collation (see db.createCollection()), the operation uses the collation specified for the collection.如果未指定排序规则，但集合具有默认排序规则（请参见db.createCollection()），则操作将使用为集合指定的排序规则。
If no collation is specified for the collection or for the operations, MongoDB uses the simple binary comparison used in prior versions for string comparisons.如果没有为集合或操作指定排序规则，MongoDB将使用以前版本中使用的简单二进制比较进行字符串比较。
You cannot specify multiple collations for an operation. 不能为一个操作指定多个排序规则。For example, you cannot specify different collations per field, or if performing a find with a sort, you cannot use one collation for the find and another for the sort. 例如，不能为每个字段指定不同的排序规则，或者如果使用排序执行查找，则不能为查找使用一个排序规则，为排序使用另一个排序顺序。

Behavior行为

In a sharded cluster, the distinct command may return orphaned documents.在分片集群中，distinct命令可能会返回孤立文档。

Array Fields数组字段

If the value of the specified field is an array, db.collection.distinct() considers each element of the array as a separate value.如果指定field的值是一个数组，那么db.collection.distinct()会将数组的每个元素视为一个单独的值。

For instance, if a field has as its value [ 1, [1], 1 ], then db.collection.distinct() considers 1, [1], and 1 as separate values.例如，如果一个字段的值为[ 1, [1], 1 ]，则db.collection.distinct()将1、[1]和1视为单独的值。

For an example, see Return Distinct Values for an Array Field.有关示例，请参阅返回数组字段的不同值。

Index Use索引使用

When possible, db.collection.distinct() operations can use indexes.如果可能，db.collection.distinct()操作可以使用索引。

Indexes can also cover db.collection.distinct() operations. 索引还可以覆盖db.collection.distinct()操作。See Covered Query for more information on queries covered by indexes.有关索引所涵盖查询的更多信息，请参阅覆盖查询。

Transactions事务

To perform a distinct operation within a transaction:要在事务中执行不同的操作：

Important

In most cases, multi-document transaction incurs a greater performance cost over single document writes, and the availability of multi-document transactions should not be a replacement for effective schema design. 在大多数情况下，与单文档写入相比，多文档事务会产生更高的性能成本，并且多文档事务的可用性不应取代有效的模式设计。For many scenarios, the denormalized data model (embedded documents and arrays) will continue to be optimal for your data and use cases. 对于许多场景，非规范化数据模型（嵌入文档和数组）将继续是您的数据和用例的最佳选择。That is, for many scenarios, modeling your data appropriately will minimize the need for multi-document transactions.也就是说，对于许多场景，对数据进行适当建模将最大限度地减少对多文档事务的需求。

For additional transactions usage considerations (such as runtime limit and oplog size limit), see also Production Considerations.有关其他事务使用注意事项（如运行时限制和操作日志大小限制），请参阅生产注意事项。

Client Disconnection客户端断开连接

Starting in MongoDB 4.2, if the client that issued db.collection.distinct() disconnects before the operation completes, MongoDB marks db.collection.distinct() for termination using killOp.从MongoDB 4.2开始，如果发出db.collection.distinct()的客户端在操作完成前断开连接，MongoDB会使用killOp标记db.collection.distinct()终止。

Replica Set Member State Restriction副本集成员状态限制

Starting in MongoDB 4.4, to run on a replica set member, distinct operations require the member to be in PRIMARY or SECONDARY state. 从MongoDB 4.4开始，要在副本集成员上运行，distinct操作需要该成员处于PRIMARY或SECONDARY状态。If the member is in another state, such as STARTUP2, the operation errors.如果成员处于其他状态，例如STARTUP2，则操作将出错。

In previous versions, the operations also run when the member is in STARTUP2. 在以前的版本中，成员处于STARTUP2时也会运行这些操作。The operations wait until the member transitioned to RECOVERING.操作将等待，直到成员转换到RECOVERING。

Examples实例

The examples use the inventory collection that contains the following documents:示例使用包含以下文档的inventory集合：

{ "_id": 1, "dept": "A", "item": { "sku": "111", "color": "red" }, "sizes": [ "S", "M" ] }
{ "_id": 2, "dept": "A", "item": { "sku": "111", "color": "blue" }, "sizes": [ "M", "L" ] }
{ "_id": 3, "dept": "B", "item": { "sku": "222", "color": "blue" }, "sizes": "S" }
{ "_id": 4, "dept": "A", "item": { "sku": "333", "color": "black" }, "sizes": [ "S" ] }

Return Distinct Values for a Field返回字段的不同值

The following example returns the distinct values for the field dept from all documents in the inventory collection:以下示例返回inventory集合中所有文档中字段dept的不同值：

db.inventory.distinct( "dept" )

The method returns the following array of distinct dept values:该方法返回以下不同dept值的数组：

[ "A", "B" ]

Return Distinct Values for an Embedded Field返回嵌入字段的不同值

The following example returns the distinct values for the field sku, embedded in the item field, from all documents in the inventory collection:以下示例返回inventory集合中所有文档中嵌入在item字段中的字段sku的不同值：

db.inventory.distinct( "item.sku" )

The method returns the following array of distinct sku values:该方法返回以下不同sku值的数组：

[ "111", "222", "333" ]
Tip

See also: 另请参阅：

Dot Notation for information on accessing fields within embedded documents有关访问嵌入文档中字段的信息的点符号

Return Distinct Values for an Array Field返回数组字段的不同值

The following example returns the distinct values for the field sizes from all documents in the inventory collection:以下示例返回inventory集合中所有文档的字段sizes的不同值：

db.inventory.distinct( "sizes" )

The method returns the following array of distinct sizes values:该方法返回以下不同sizes值的数组：

[ "M", "S", "L" ]

For information on distinct() and array fields, see the Behavior section.有关distinct()和数组字段的信息，请参阅行为部分。

Specify Query with distinct使用distinct指定查询

The following example returns the distinct values for the field sku, embedded in the item field, from the documents whose dept is equal to "A":以下示例从dept等于"A"的文档中返回嵌入在item字段中的字段sku的不同值：

db.inventory.distinct( "item.sku", { dept: "A" } )

The method returns the following array of distinct sku values:该方法返回以下不同sku值的数组：

[ "111", "333" ]

Specify a Collation指定排序规则

Collation allows users to specify language-specific rules for string comparison, such as rules for lettercase and accent marks.排序规则允许用户为字符串比较指定特定于语言的规则，例如大小写和重音标记的规则。

A collection myColl has the following documents:集合myColl包含以下文档：

{ _id: 1, category: "café", status: "A" }
{ _id: 2, category: "cafe", status: "a" }
{ _id: 3, category: "cafE", status: "a" }

The following aggregation operation includes the Collation option:以下聚合操作包括排序规则选项：

db.myColl.distinct( "category", {}, { collation: { locale: "fr", strength: 1 } } )

For descriptions on the collation fields, see Collation Document.有关排序规则字段的说明，请参阅排序规则文档。