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- $count (aggregation)
$count (aggregation)¶
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Definition¶
-
$count
¶ Returns a document that contains a count of the number of documents input to the stage.
$count
has the following prototype form:<string>
is the name of the output field which has the count as its value.<string>
must be a non-empty string, must not start with$
and must not contain the.
character.
Example¶
A collection named scores
has the following documents:
The following aggregation operation has two stages:
- The
$match
stage excludes documents that have ascore
value of less than or equal to80
to pass along the documents withscore
greater than80
to the next stage. - The
$count
stage returns a count of the remaining documents in the aggregation pipeline and assigns the value to a field calledpassing_scores
.
The operation returns the following results: