如何在 MongoDB 中获取最大值和最小值？答案

【问题标题】：How to get Max and Min Value in MongoDB?如何在 MongoDB 中获取最大值和最小值？
【发布时间】：2021-11-08 17:52:28
【问题描述】：

我想获取基于货币的 emp 工资的最大值和最小值。每个员工都有一个基于货币的工资范围，所有响应的细节都应该是唯一的。虽然我使用聚合函数 min 和 max 但它获取工资金额的最大值和最小值，但我需要根据货币字段获取最大值和最小值。

样本数据：

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

预期输出：城市、国家/地区，名称应该是唯一的，并且薪水具有基于货币的最大值和最小值。

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

【问题讨论】：

标签： java mongodb

【解决方案1】：

我们可以$group 两次来实现这一点，一次为每个员工 x 货币计算最小值和最大值，然后再次不使用货币来构建最终结构，如下所示：

db.collection.aggregate([
  {
    $unwind: "$data"
  },
  {
    $unwind: "$data.salary"
  },
  {
    $addFields: {
      currency: {
        "$objectToArray": "$data.salary"
      }
    }
  },
  {
    $unwind: "$currency"
  },
  {
    $group: {
      _id: {
        country: "$data.emp_country",
        city: "$data.emp_city",
        emp_name: "$emp_name",
        currency: "$currency.k"
      },
      max: {
        $max: "$currency.v"
      },
      min: {
        $min: "$currency.v"
      },
      
    }
  },
  {
    $group: {
      _id: {
        country: "$_id.country",
        city: "$_id.city",
        emp_name: "$_id.emp_name",
        
      },
      emp_salary: {
        $push: {
          currency: "$_id.currency",
          max: "$max",
          min: "$min"
        }
      }
    }
  },
  {
    $project: {
      emp_salary: 1,
      emp_country: "$_id.country",
      emp_city: "$_id.city",
      emp_name: "$_id.emp_name",
      _id: 0
    }
  }
])

Mongo Playground

【讨论】：