db.collection.distinct()
MongoDB with drivers
This page documents a mongosh method. To see the equivalent
method in a MongoDB driver, see the corresponding page for your
programming language:
Definition
Compatibility
This method is available in deployments hosted in the following environments:
MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud
Note
This command is supported in all MongoDB Atlas clusters. For information on Atlas support for all commands, see Unsupported Commands.
MongoDB Enterprise: The subscription-based, self-managed version of MongoDB
MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB
Syntax
This method takes the following parameters:
Parameter | Type | Description |
|---|---|---|
| string | The field for which to return distinct values. |
| document | A query that specifies the documents from which to retrieve the distinct values. |
| document | Optional. A document that specifies the options. See Options. |
Note
Results must not be larger than the maximum BSON size. 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.
The following diagram shows an example
db.collection.distinct() call.
Options
{ collation: <document> }
Field | Type | Description | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| document | Optional. Specifies the collation to use for the operation. Collation allows users to specify language-specific rules for string comparison, such as rules for lettercase and accent marks. The collation option has the following syntax: When specifying collation, the If the collation is unspecified but the collection has a
default collation (see 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. You cannot specify multiple collations for an operation. 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. |
Behavior
In a sharded cluster, the distinct command may return
orphaned documents.
For time series collections, the
distinct command can't make efficient use of indexes. Instead, use a
$group aggregation to group documents by distinct values. For
details, see Time Series Limitations.
Array Fields
If the value of the specified field is an array,
db.collection.distinct() considers each element of the array
as a separate value.
For instance, if a field has as its value [ 1, [1], 1 ], then
db.collection.distinct() considers 1, [1], and 1 as separate values.
For an example, see Return Distinct Values for an Array Field.
Index Use
When possible, db.collection.distinct() operations can use indexes.
Indexes can also cover
db.collection.distinct() operations. See Covered Query for more information
on queries covered by indexes.
Transactions
To perform a distinct operation within a transaction:
For unsharded collections, you can use the
db.collection.distinct()method/thedistinctcommand as well as the aggregation pipeline with the$groupstage.For sharded collections, you cannot use the
db.collection.distinct()method or thedistinctcommand.To find the distinct values for a sharded collection, use the aggregation pipeline with the
$groupstage instead. See Distinct Operation for details.
Important
In most cases, a distributed transaction incurs a greater performance cost over single document writes, and the availability of distributed transactions should not be a replacement for effective schema design. For many scenarios, the denormalized data model (embedded documents and arrays) will continue to be optimal for your data and use cases. That is, for many scenarios, modeling your data appropriately will minimize the need for distributed transactions.
For additional transactions usage considerations (such as runtime limit and oplog size limit), see also Production Considerations.
Client Disconnection
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.
Replica Set Member State Restriction
To run on a replica set member, distinct operations require the member
to be in PRIMARY or SECONDARY state. If the member
is in another state, such as STARTUP2, the
operation errors.
Query Settings
New in version 8.0.
You can use query settings to set index hints, set operation rejection filters, and other fields. The settings apply to the query shape on the entire cluster. The cluster retains the settings after shutdown.
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.
To add query settings and explore examples, see
setQuerySettings.
You can add query settings for find, distinct,
and aggregate commands.
Query settings have more functionality and are preferred over deprecated index filters.
To remove query settings, use removeQuerySettings. To
obtain the query settings, use a $querySettings stage in an
aggregation pipeline.
Examples
The examples use the inventory collection that contains the
following documents:
{ "_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
The following example returns the distinct values for the field
dept from all documents in the inventory collection:
db.inventory.distinct( "dept" )
The method returns the following array of distinct dept values:
[ "A", "B" ]
Return Distinct Values for an Embedded Field
The following example returns the distinct values for the field
sku, embedded in the item field, from all documents in the
inventory collection:
db.inventory.distinct( "item.sku" )
The method returns the following array of distinct sku values:
[ "111", "222", "333" ]
Return Distinct Values for an Array Field
The following example returns the distinct values for the field
sizes from all documents in the inventory collection:
db.inventory.distinct( "sizes" )
The method returns the following array of distinct sizes values:
[ "M", "S", "L" ]
For information on distinct() and array
fields, see the Behavior section.
Specify Query with distinct
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":
db.inventory.distinct( "item.sku", { dept: "A" } )
The method returns the following array of distinct sku values:
[ "111", "333" ]
Specify a Collation
Collation allows users to specify language-specific rules for string comparison, such as rules for lettercase and accent marks.
A collection myColl has the following documents:
{ _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:
db.myColl.distinct( "category", {}, { collation: { locale: "fr", strength: 1 } } )
For descriptions on the collation fields, see Collation Document.