count¶

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Definition
Behavior
Examples

Definition¶

count¶

Counts the number of documents in a collection. Returns a document that contains this count and as well as the command status. count has the following form:

Changed in version 2.6: count now accepts the hint option to specify an index.

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{ count: <collection>, query: <query>, limit: <limit>, skip: <skip>, hint: <hint> }

count has the following fields:

Field	Type	Description
`count`	string	The name of the collection to count.
`query`	document	Optional. A query that selects which documents to count in a collection.
`limit`	integer	Optional. The maximum number of matching documents to return.
`skip`	integer	Optional. The number of matching documents to skip before returning results.
`hint`	String or document	Optional. The index to use. Specify either the index name as a string or the index specification document. New in version 2.6.

MongoDB also provides the count() and db.collection.count() wrapper methods in the mongo shell.

Behavior¶

On a sharded cluster, count can result in an inaccurate count if orphaned documents exist or if a chunk migration is in progress.

To avoid these situations, on a sharded cluster, use the $group stage of the db.collection.aggregate() method to $sum the documents. For example, the following operation counts the documents in a collection:

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db.collection.aggregate(
   [
      { $group: { _id: null, count: { $sum: 1 } } }
   ]
)

To get a count of documents that match a query condition, include the $match stage as well:

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db.collection.aggregate(
   [
      { $match: <query condition> },
      { $group: { _id: null, count: { $sum: 1 } } }
   ]
)

See Perform a Count for an example.

Examples¶

The following sections provide examples of the count command.

Count All Documents¶

The following operation counts the number of all documents in the orders collection:

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db.runCommand( { count: 'orders' } )

In the result, the n, which represents the count, is 26, and the command status ok is 1:

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{ "n" : 26, "ok" : 1 }

Count Documents That Match a Query¶

The following operation returns a count of the documents in the orders collection where the value of the ord_dt field is greater than Date('01/01/2012'):

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db.runCommand( { count:'orders',
                 query: { ord_dt: { $gt: new Date('01/01/2012') } }
               } )

In the result, the n, which represents the count, is 13 and the command status ok is 1:

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{ "n" : 13, "ok" : 1 }

Skip Documents in Count¶

The following operation returns a count of the documents in the orders collection where the value of the ord_dt field is greater than Date('01/01/2012') and skip the first 10 matching documents:

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db.runCommand( { count:'orders',
                 query: { ord_dt: { $gt: new Date('01/01/2012') } },
                 skip: 10 }  )

In the result, the n, which represents the count, is 3 and the command status ok is 1:

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{ "n" : 3, "ok" : 1 }

Specify the Index to Use¶

The following operation uses the index { status: 1 } to return a count of the documents in the orders collection where the value of the ord_dt field is greater than Date('01/01/2012') and the status field is equal to "D":

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db.runCommand(
   {
     count:'orders',
     query: {
              ord_dt: { $gt: new Date('01/01/2012') },
              status: "D"
            },
     hint: { status: 1 }
   }
)

In the result, the n, which represents the count, is 1 and the command status ok is 1:

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{ "n" : 1, "ok" : 1 }

← aggregate distinct →