需要根据mongodb中的值来统计字段

{
  "_id": 1,
  "customer_id": 1,
  "amount": 100,
  "status": "completed"
},
{
  "_id": 2,
  "customer_id": 1,
  "amount": 200,
  "status": "completed"
},
{
  "_id": 3,
  "customer_id": 2,
  "amount": 300,
  "status": "pending"
}

db.orders.aggregate([
  {
    $match: {
      "status": "completed"
    }
  },
  {
    $group: {
      _id: "$customer_id",
      totalAmount: { $sum: "$amount" }
    }
  }
])

{
  "_id": 1,
  "totalAmount": 300
}

db.orders.aggregate([
  {
    $group: {
      _id: "$customer_id",
      totalAmount: { $sum: "$amount" }
    }
  }
])