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- db.collection.distinct()
db.collection.distinct()¶
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Definition¶
-
db.collection.
distinct
(field, query)¶ Finds the distinct values for a specified field across a single collection and returns the results in an array.
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. The
db.collection.distinct()
method provides a wrapper around thedistinct
command. Results must not be larger than the maximum BSON size.
Behavior¶
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.
Examples¶
The examples use the inventory
collection that contains the
following documents:
Return Distinct Values for a Field¶
The following example returns the distinct values for the field
dept
from all documents in the inventory
collection:
The method returns the following array of distinct dept
values:
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:
The method returns the following array of distinct sku
values:
See also
Dot Notation for information on accessing fields within embedded documents
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:
The method returns the following array of distinct sizes
values:
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"
:
The method returns the following array of distinct sku
values: