MongoDB聚合简单查询

我有以下MongoDB数据示例：

{"FirstName": "Bruce", "LastName": "Wayne", 
"Email": "bwayne@Wayneenterprises.com"}
{"FirstName": "Lucius", "LastName": "Fox", 
"Email": "lfox@Wayneenterprises.com"}
{"FirstName": "Dick", "LastName": "Grayson", 
"Email": "dgrayson@Wayneenterprises.com"}

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我想得到并找到所有文档的计数可能是这样的：

   db.col.aggregate([  {$match:{  "Bed Grade":4}}  , {  $group: {_id:{h:"$Hospital_code" ,d:"$Department" } , cnt:{$sum:1}} }  , {$match:{cnt:{$gt:5}}}  ])

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非常感谢。我可以再问一个问题吗？