db.collection.distinct()
Definition
db.collection.distinct(field, query, options)
Important
mongo Shell Method
This page documents a
mongo
method. This is not the documentation for database commands or language-specific drivers, such as Node.js. To use the database command, see thedistinct
command.For MongoDB API drivers, refer to the language-specific MongoDB driver documentation.
Finds the distinct values for a specified field across a single collection or view and returns the results in an array.
Compatibility
You can use db.collection.distinct()
for deployments hosted in the following
environments:
MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud
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 |
---|---|---|
field | string | The field for which to return distinct values. |
query | document | A query that specifies the documents from which to retrieve the distinct values. |
options | 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 $group
operator, as described in
Retrieve Distinct Values with the Aggregation Pipeline.
Options
{ collation: <document> }
Field | Type | Description | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
collation | document | Optional. Specifies the collation to use for the operation. Collation allows users to specify language-specific rules for string comparison, such as rules for lettercase and accent marks. The collation option has the following syntax:
When specifying collation, the If the collation is unspecified but the collection has a
default collation (see If no collation is specified for the collection or for the operations, MongoDB uses the simple binary comparison used in prior versions for string comparisons. You cannot specify multiple collations for an operation. For example, you cannot specify different collations per field, or if performing a find with a sort, you cannot use one collation for the find and another for the sort. New in version 3.4. |
Behavior
In a sharded cluster, the distinct
command may return
orphaned documents.
Array Fields
If the value of the specified field
is an array,
db.collection.distinct()
considers each element of the array
as a separate value.
For instance, if a field has as its value [ 1, [1], 1 ]
, then
db.collection.distinct()
considers 1
, [1]
, and 1
as separate values.
For an example, see Return Distinct Values for an Array Field.
Index Use
When possible, db.collection.distinct()
operations can use indexes.
Indexes can also cover
db.collection.distinct()
operations. See Covered Query for more information
on queries covered by indexes.
Transactions
To perform a distinct operation within a transaction:
For unsharded collections, you can use the
db.collection.distinct()
method/thedistinct
command as well as the aggregation pipeline with the$group
stage.For sharded collections, you cannot use the
db.collection.distinct()
method or thedistinct
command.To find the distinct values for a sharded collection, use the aggregation pipeline with the
$group
stage 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
Starting in MongoDB 4.4, 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.
In previous versions, the operations also run when the member
is in STARTUP2
. The operations wait until the member
transitioned to RECOVERING
.
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
New in version 3.4.
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.