How to get Max and Min Value in MongoDB based on specific key?

Question

I want to get the max and min value of the emp salary based on currency. every employee has a salary range based on currency also all the details in response should be unique. while I am using aggregation function min and max but it fetches the max and min value of salary amount but I need to get max and min based on currency field.

Sample Data:

[
  {
    "id": "1",
    "emp_name": "emp1",
    "data": [
      {
        "emp_country": "country1",
        "emp_city": "city1",
        "salary": [
          {
            "currency": "INR",
            "amount": 5000
          },
          {
            "currency": "INR",
            "amount": 600
          },
          {
            "currency": "MXN",
            "amount": 400
          }
        ]
      },
      {
        "emp_country": "country1",
        "emp_city": "city2",
        "salary": [
          {
            "currency": "DOLLER",
            "amount": 5000
          },
          {
            "currency": "DOLLER",
            "amount": 200
          },
          {
            "currency": "MXN",
            "amount": 400
          }
        ]
      }
    ]
  },
  {
    "id": "2",
    "emp_name": "emp2",
    "data": [
      {
        "emp_country": "country2",
        "emp_city": "city2",
        "salary": [
          {
            "currency": "INR",
            "amount": 5000
          },
          {
            "currency": "MXN",
            "amount": 200
          },
          {
            "currency": "MXN",
            "amount": 400
          }
        ]
      }
    ]
  },
  {
    "id": "3",
    "emp_name": "emp3",
    "data": [
      {
        "emp_country": "country1",
        "emp_city": "city1",
        "salary": [
          {
            "currency": "MXN",
            "amount": 400
          }
        ]
      }
    ]
  },
  {
    "id": "4",
    "emp_name": "emp4",
    "data": [
      {
        "emp_country": "country1",
        "emp_city": "city2",
        "salary": [
          {
            "currency": "DOLLER",
            "amount": 200
          }
        ]
      }
    ]
  }
]

Expected Output: city, country, the name should be unique and salary have max and min based on currency.

[
  {
    "emp_city": "city1",
    "emp_country": "country1",
    "emp_name": "emp1",
    "emp_salary": [{
      "currency": "INR",
      "max": 5000,
      "min": 600
    },
    {
      "currency": "MXN",
      "max": 400,
      "min": 400
    }]
  },
  {
    "emp_city": "city2",
    "emp_country": "country1",
    "emp_name": "emp1",
    "emp_salary":[ {
      "currency": "DOLLER",
      "max": 5000,
      "min": 200
    },
    {
      "currency": "MXN",
      "max": 400,
      "min": 400
    }]
  },
  {
    "emp_city": "city2",
    "emp_country": "country2",
    "emp_name": "emp2",
    "emp_salary": [{
      "currency": "INR",
      "max": 5000,
      "min": 5000
    },
    {
      "currency": "MXN",
      "max": 400,
      "min": 200
    }]
  },
  {
    "emp_city": "city1",
    "emp_country": "country1",
    "emp_name": "emp3",
    "emp_salary": [{
      "currency": "MXN",
      "max": 400,
      "min": 400
    }]
  },
  {
    "emp_city": "city2",
    "emp_country": "country1",
    "emp_name": "emp4",
    "emp_salary": [{
      "currency": "DOLLER",
      "max": 200,
      "min": 200
    }]
  }
]

your sample data is one doc in your collection or there are multiple doc in collection — mohammad Naimi
– mohammad Naimi, Commented Aug 31, 2021 at 9:16
@mohammadNaimi sample data is 4 doc in the collection while id is manually generated rather than automatic. — prabhakar srivastava
– prabhakar srivastava, Commented Aug 31, 2021 at 10:16

turivishal · Accepted Answer · 2021-09-01 05:19:13Z

We can achieve the above result using an aggregation query.

$unwind - to deconstruct array of salary
$group - group by emp city, country, name, currency with min and max value of salary
$group - use another to push in emp_salary
$project - to show fields in your format

db.collection.aggregate([
  {
    "$unwind": {
      "path": "$data"
    }
  },
  {
    "$unwind": {
      "path": "$data.salary"
    }
  },
  {
    "$group": {
      "_id": {
        "emp_city": "$data.emp_city",
        "emp_country": "$data.emp_country",
        "emp_name": "$emp_name",
        "currency": "$data.salary.currency",
        
      },
      "max": {
        "$max": "$data.salary.amount"
      },
      "min": {
        "$min": "$data.salary.amount"
      }
    }
  },
  {
    "$group": {
      "_id": {
        "emp_city": "$_id.emp_city",
        "emp_country": "$_id.emp_country",
        "emp_name": "$_id.emp_name",
        
      },
      "emp_salary": {
        "$push": {
          "currency": "$_id.currency",
          "min": "$min",
          "max": "$max"
        }
      }
    }
  },
  {
    "$project": {
      "_id": 0,
      "emp_city": "$_id.emp_city",
      "emp_country": "$_id.emp_country",
      "emp_name": "$_id.emp_name",
      "emp_salary": 1,
      
    }
  }
])

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