MongoDB 查询仅显示大于平均值的数据

Question

DEMO https://mongoplayground.net/p/ImiJWm1s-lx

db={
  BRANCH: [
    {
      "BCODE": "B1",
      "BNAME": "CANADA"
    },
    {
      "BCODE": "B2",
      "BNAME": "USA"
    },
    {
      "BCODE": "B3",
      "BNAME": "CANADA"
    }
  ],
  ACCOUNT: [
    {
      "ANO": 1,
      "Amount": 1000,
      "BCODE": "B1"
    },
    {
      "ANO": 2,
      "Amount": 350,
      "BCODE": "B1"
    },
    {
      "ANO": 3,
      "Amount": 450,
      "BCODE": "B1"
    },
    {
      "ANO": 4,
      "Amount": 360,
      "BCODE": "B2"
    },
    {
      "ANO": 5,
      "Amount": 800,
      "BCODE": "B2"
    },
    {
      "ANO": 6,
      "Amount": 450,
      "BCODE": "B3"
    },
    {
      "ANO": 7,
      "Amount": 360,
      "BCODE": "B2"
    },
    {
      "ANO": 8,
      "Amount": 800,
      "BCODE": "B1"
    }
  ]
}

I have this MongoDB collection. I am able to show no of accounts in each branch Using This Query :

db.BRANCH.aggregate([
  {
    $lookup: {
      from: "ACCOUNT",
      localField: "BCODE",
      foreignField: "BCODE",
      as: "TOTAL_ACCOUNTS"
    }
  },
  {
    "$addFields": {
      "TOTAL ACCOUNTS": {
        $size: "$TOTAL_ACCOUNTS"
      }
    }
  },
  {
    "$project": {
      _id: 0,
      TOTAL_ACCOUNTS: 0
    }
  }
])

OUTPUT

[
  {
    "BCODE": "B1",
    "BNAME": "CANADA",
    "TOTAL ACCOUNTS": 4
  },
  {
    "BCODE": "B2",
    "BNAME": "USA",
    "TOTAL ACCOUNTS": 3
  },
  {
    "BCODE": "B3",
    "BNAME": "CANADA",
    "TOTAL ACCOUNTS": 1
  }
]

but I need to show only those branch details where No. of accounts is more than an average number of accounts in all branches.

So according to the given data AVG Accounts of all branches is (4+3+1)/3 = 2

It means Only Branch B1 & Branch B2 should be displayed because they have 4 accounts and 3 accounts respectively.

Branch B3 should not be displayed because It has only 1 Account & 1<2 (Avg No of account).

What should i use here?

Answer 1

• $group by null and construct the array of branches and get the average of the total size of accounts
• $filter to iterate loop of branches array and check condition that total should greater than average of the total size of accounts

db.BRANCH.aggregate([
  {
    $lookup: {
      from: "ACCOUNT",
      localField: "BCODE",
      foreignField: "BCODE",
      as: "TOTAL_ACCOUNTS"
    }
  },
  { $addFields: { TOTAL_ACCOUNTS: { $size: "$TOTAL_ACCOUNTS" } } },
  {
    $group: {
      _id: null,
      branches: { $push: "$$ROOT" },
      totalAvg: { $avg: "$TOTAL_ACCOUNTS" }
    }
  },
  {
    $project: {
      _id: 0,
      branches: {
        $filter: {
          input: "$branches",
          cond: { $gt: ["$$this.TOTAL_ACCOUNTS", "$totalAvg"] }
        }
      }
    }
  }
])

Playground