db.collection.distinct() (mongosh method方法)

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，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.例如，请参阅返回数组字段的不重复值。

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. 索引还可以涵盖db.collection.distinct()操作。See Run Covered Queries for more information on queries covered by indexes.有关索引覆盖的查询的更多信息，请参阅运行覆盖的查询。

Transactions事务

To perform a distinct operation within a transaction:要在事务中执行distinct操作，请执行以下操作：

• For unsharded collections, you can use the db.collection.distinct() method/the distinct command as well as the aggregation pipeline with the $group stage.对于未记录的集合，您可以使用db.collection.distinct()方法/distinct命令以及$group阶段的聚合管道。

• For sharded collections, you cannot use the db.collection.distinct() method or the distinct command.对于分片集合，不能使用db.collection.distinct()方法或distinct命令。

  To find the distinct values for a sharded collection, use the aggregation pipeline with the $group stage instead. 要查找分片集合的不重复值，请使用带有$group阶段的聚合管道。See Distinct Operation for details.详见Distinct操作。

Client Disconnection客户端断开连接

If the client that issued db.collection.distinct() disconnects before the operation completes, MongoDB marks db.collection.distinct() for termination using killOp.如果发出db.collection.distinct()的客户端在操作完成之前断开连接，MongoDB将使用killOp标记db.collection.distinct()以终止。

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

To run on a replica set member, distinct operations require the member to be in PRIMARY or SECONDARY state. 要在副本集成员上运行，distinct操作要求该成员处于PRIMARY或SECONDARY状态。If the member is in another state, such as STARTUP2, the operation errors.如果成员处于另一种状态，如STARTUP2，则操作错误。

Query Settings查询设置

You can use query settings to set index hints, set operation rejection filters, and other fields. 您可以使用查询设置来设置索引提示、设置操作拒绝筛选器和其他字段。The settings apply to the query shape on the entire cluster. The cluster retains the settings after shutdown.这些设置适用于整个集群上的查询形状。集群在关闭后保留设置。

The query optimizer uses the query settings as an additional input during query planning, which affects the plan selected to run the query. You can also use query settings to block a query shape.查询优化器在查询规划期间使用查询设置作为额外输入，这会影响选择运行查询的计划。您还可以使用查询设置来阻止查询形状。

To add query settings and explore examples, see setQuerySettings.要添加查询设置并探索示例，请参阅setQuerySettings。

You can add query settings for find, distinct, and aggregate commands.您可以为find、distinct和aggregate命令添加查询设置。

Query settings have more functionality and are preferred over deprecated index filters.查询设置具有更多功能，并且优于已弃用的索引筛选器。

To remove query settings, use removeQuerySettings. To obtain the query settings, use a $querySettings stage in an aggregation pipeline.要删除查询设置，请使用removeQuerySettings。要获取查询设置，请在聚合管道中使用$querySettings阶段。

Return Distinct Values for a Field为字段返回非重复的值

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集合中所有文档的字段dept的不重复值：

db.inventory.distinct( "dept" )

The method returns the following array of unique dept values:该方法返回以下唯一dept值数组：

[ "A", "B" ]

Return Distinct Values for an Embedded Field为嵌入式字段返回非重复的值

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的不重复值：

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

The method returns the following array of unique sku values:该方法返回以下唯一sku值数组：

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

Return Distinct Values for an Array Field为数组字段返回非重复的值

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大小的不重复值：

db.inventory.distinct( "sizes" )

The method returns the following array of unique sizes values:该方法返回以下唯一sizes值数组：

[ "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的不重复值：

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

The method returns the following array of unique sku values:该方法返回以下唯一sku值数组：

[ "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，例如字母大小写和重音标记的规则。

A collection myColl has the following documents:myColl集合有以下文件：

db.myColl.insertMany( [
   { _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。