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运算符

$rank（聚合）

在本页

  • 定义
  • 行为
  • 示例

定义

新版本5.0.

$rank

返回文档位置（称为排名）相对于$setWindowFields阶段的分区。

在sortBy字段值中，$setWindowFields阶段确定文档的排名。当与$rank运算符一起使用时，sortBy只能将其值设置为单个字段。有关MongoDB如何比较不同类型的字段的更多信息，请参阅BSON比较顺序。

如果有多个文档占据相同的排名，$rank将具有后续值的文档放置在带有间隔的排名中（请参阅行为）。

$rank仅在$setWindowFields阶段可用。

$rank语法

{ $rank: { } }

$rank不接受任何参数。

提示

另请参阅

$denseRank

行为

  • $rank和$denseRank在如何对重复的sortBy字段值进行排名方面有所不同。例如，当sortBy字段值为7, 9, 9, 和10时

    • $denseRank将值排名为1, 2, 2, 和3。重复的9值具有排名2，而10具有排名3。排名之间没有间隔。

    • $rank将值排名为1, 2, 2, 和4。重复的9值具有排名2，而10具有排名4。排名3处存在间隔。

  • 具有sortBy字段值为null的文档或缺少sortBy字段的文档将根据BSON比较顺序分配排名。请参阅包含重复值、空值或缺失数据的排名分区示例。

  • 从MongoDB 8.0版本开始，在$denseRank和$rank的sortBy操作中，对null和缺失的字段值进行相同的处理。这一变更使得denseRank和rank的行为与$sort操作保持一致。

示例

创建一个包含加利福尼亚（CA）和华盛顿（WA）州蛋糕销售的cakeSales集合

db.cakeSales.insertMany( [
   { _id: 0, type: "chocolate", orderDate: new Date("2020-05-18T14:10:30Z"),
     state: "CA", price: 13, quantity: 120 },
   { _id: 1, type: "chocolate", orderDate: new Date("2021-03-20T11:30:05Z"),
     state: "WA", price: 14, quantity: 140 },
   { _id: 2, type: "vanilla", orderDate: new Date("2021-01-11T06:31:15Z"),
     state: "CA", price: 12, quantity: 145 },
   { _id: 3, type: "vanilla", orderDate: new Date("2020-02-08T13:13:23Z"),
     state: "WA", price: 13, quantity: 104 },
   { _id: 4, type: "strawberry", orderDate: new Date("2019-05-18T16:09:01Z"),
     state: "CA", price: 41, quantity: 162 },
   { _id: 5, type: "strawberry", orderDate: new Date("2019-01-08T06:12:03Z"),
     state: "WA", price: 43, quantity: 134 }
] )

按整数字段对分区进行排名

本例使用$rank在$setWindowFields阶段中，输出每个state的蛋糕销售的quantity排名。

db.cakeSales.aggregate( [
   {
      $setWindowFields: {
         partitionBy: "$state",
         sortBy: { quantity: -1 },
         output: {
            rankQuantityForState: {
               $rank: {}
            }
         }
      }
   }
] )

在示例中

  • partitionBy: "$state" 分区集合中的文档，按state进行分区。有CA和WA的分区。

  • sortBy: { quantity: -1 } 排序每个分区的文档，按quantity降序（-1），因此最高的quantity排在第一位。

  • output将rankQuantityForState字段设置为使用$rank的quantity排名，如下所示的结果。

{ "_id" : 4, "type" : "strawberry", "orderDate" : ISODate("2019-05-18T16:09:01Z"),
  "state" : "CA", "price" : 41, "quantity" : 162, "rankQuantityForState" : 1 }
{ "_id" : 2, "type" : "vanilla", "orderDate" : ISODate("2021-01-11T06:31:15Z"),
  "state" : "CA", "price" : 12, "quantity" : 145, "rankQuantityForState" : 2 }
{ "_id" : 0, "type" : "chocolate", "orderDate" : ISODate("2020-05-18T14:10:30Z"),
  "state" : "CA", "price" : 13, "quantity" : 120, "rankQuantityForState" : 3 }
{ "_id" : 1, "type" : "chocolate", "orderDate" : ISODate("2021-03-20T11:30:05Z"),
  "state" : "WA", "price" : 14, "quantity" : 140, "rankQuantityForState" : 1 }
{ "_id" : 5, "type" : "strawberry", "orderDate" : ISODate("2019-01-08T06:12:03Z"),
  "state" : "WA", "price" : 43, "quantity" : 134, "rankQuantityForState" : 2 }
{ "_id" : 3, "type" : "vanilla", "orderDate" : ISODate("2020-02-08T13:13:23Z"),
  "state" : "WA", "price" : 13, "quantity" : 104, "rankQuantityForState" : 3 }

按日期字段对分区进行排序

此示例展示了如何在$rank中与$setWindowFields阶段一起使用日期，以输出每个state的蛋糕销售的orderDate排名。

db.cakeSales.aggregate( [
   {
      $setWindowFields: {
         partitionBy: "$state",
         sortBy: { orderDate: 1 },
         output: {
            rankOrderDateForState: {
               $rank: {}
            }
         }
      }
   }
] )

在示例中

  • partitionBy: "$state" 分区集合中的文档，按state进行分区。有CA和WA的分区。

  • sortBy: { orderDate: 1 } 排序每个分区内的文档，按orderDate升序（1），因此最早的orderDate排在第一位。

  • output使用$rank将rankOrderDateForState字段设置为orderDate排名，如下所示的结果。

{ "_id" : 4, "type" : "strawberry", "orderDate" : ISODate("2019-05-18T16:09:01Z"),
  "state" : "CA", "price" : 41, "quantity" : 162, "rankOrderDateForState" : 1 }
{ "_id" : 0, "type" : "chocolate", "orderDate" : ISODate("2020-05-18T14:10:30Z"),
  "state" : "CA", "price" : 13, "quantity" : 120, "rankOrderDateForState" : 2 }
{ "_id" : 2, "type" : "vanilla", "orderDate" : ISODate("2021-01-11T06:31:15Z"),
  "state" : "CA", "price" : 12, "quantity" : 145, "rankOrderDateForState" : 3 }
{ "_id" : 5, "type" : "strawberry", "orderDate" : ISODate("2019-01-08T06:12:03Z"),
  "state" : "WA", "price" : 43, "quantity" : 134, "rankOrderDateForState" : 1 }
{ "_id" : 3, "type" : "vanilla", "orderDate" : ISODate("2020-02-08T13:13:23Z"),
  "state" : "WA", "price" : 13, "quantity" : 104, "rankOrderDateForState" : 2 }
{ "_id" : 1, "type" : "chocolate", "orderDate" : ISODate("2021-03-20T11:30:05Z"),
  "state" : "WA", "price" : 14, "quantity" : 140, "rankOrderDateForState" : 3 }

包含重复值、空值或缺失数据的分区排名

创建一个cakeSalesWithDuplicates集合，其中

  • 蛋糕销售发生在加利福尼亚州（CA）和华盛顿州（WA）。

  • 文档6到8的quantity和state与文档5相同。

  • 文档9的quantity和state与文档4相同。

  • 文档10的quantity是空值。

  • 文档11缺少quantity。

db.cakeSalesWithDuplicates.insertMany( [
   { _id: 0, type: "chocolate", orderDate: new Date("2020-05-18T14:10:30Z"),
     state: "CA", price: 13, quantity: 120 },
   { _id: 1, type: "chocolate", orderDate: new Date("2021-03-20T11:30:05Z"),
     state: "WA", price: 14, quantity: 140 },
   { _id: 2, type: "vanilla", orderDate: new Date("2021-01-11T06:31:15Z"),
     state: "CA", price: 12, quantity: 145 },
   { _id: 3, type: "vanilla", orderDate: new Date("2020-02-08T13:13:23Z"),
     state: "WA", price: 13, quantity: 104 },
   { _id: 4, type: "strawberry", orderDate: new Date("2019-05-18T16:09:01Z"),
     state: "CA", price: 41, quantity: 162 },
   { _id: 5, type: "strawberry", orderDate: new Date("2019-01-08T06:12:03Z"),
     state: "WA", price: 43, quantity: 134 },
   { _id: 6, type: "strawberry", orderDate: new Date("2020-01-08T06:12:03Z"),
     state: "WA", price: 41, quantity: 134 },
   { _id: 7, type: "strawberry", orderDate: new Date("2020-01-01T06:12:03Z"),
     state: "WA", price: 34, quantity: 134 },
   { _id: 8, type: "strawberry", orderDate: new Date("2020-01-02T06:12:03Z"),
     state: "WA", price: 40, quantity: 134 },
   { _id: 9, type: "strawberry", orderDate: new Date("2020-05-11T16:09:01Z"),
     state: "CA", price: 39, quantity: 162 },
   { _id: 10, type: "strawberry", orderDate: new Date("2020-05-11T16:09:01Z"),
     state: "CA", price: 39, quantity: null },
   { _id: 11, type: "strawberry", orderDate: new Date("2020-05-11T16:09:01Z"),
     state: "CA", price: 39 }
] )

本例在$rank阶段使用$setWindowFields，以输出每个state的来自cakeSalesWithDuplicates集合的quantity排名。

db.cakeSalesWithDuplicates.aggregate( [
   {
      $setWindowFields: {
         partitionBy: "$state",
         sortBy: { quantity: -1 },
         output: {
            rankQuantityForState: {
               $rank: {}
            }
         }
      }
   }
] )

在示例中

  • partitionBy: "$state" 分区集合中的文档，按state进行分区。有CA和WA的分区。

  • sortBy: { quantity: -1 } 排序每个分区的文档，按quantity降序（-1），因此最高的quantity排在第一位。

以下示例输出

  • 具有相同quantity和state的文档具有相同的排名。如果文档具有相同的排名，则该排名与下一个排名之间存在空缺。

  • 在输出中，具有null quantity的文档和缺少quantity的文档在CA分区中被排在最低。这种排序是BSON比较顺序的结果，在这个例子中将null和缺失值排序在数字值之后。

{ "_id" : 4, "type" : "strawberry", "orderDate" : ISODate("2019-05-18T16:09:01Z"),
  "state" : "CA", "price" : 41, "quantity" : 162, "rankQuantityForState" : 1 }
{ "_id" : 9, "type" : "strawberry", "orderDate" : ISODate("2020-05-11T16:09:01Z"),
  "state" : "CA", "price" : 39, "quantity" : 162, "rankQuantityForState" : 1 }
{ "_id" : 2, "type" : "vanilla", "orderDate" : ISODate("2021-01-11T06:31:15Z"),
  "state" : "CA", "price" : 12, "quantity" : 145, "rankQuantityForState" : 3 }
{ "_id" : 0, "type" : "chocolate", "orderDate" : ISODate("2020-05-18T14:10:30Z"),
  "state" : "CA", "price" : 13, "quantity" : 120, "rankQuantityForState" : 4 }
{ "_id" : 10, "type" : "strawberry", "orderDate" : ISODate("2020-05-11T16:09:01Z"),
  "state" : "CA", "price" : 39, "quantity" : null, "rankQuantityForState" : 5 }
{ "_id" : 11, "type" : "strawberry", "orderDate" : ISODate("2020-05-11T16:09:01Z"),
  "state" : "CA", "price" : 39, "rankQuantityForState" : 5 }
{ "_id" : 1, "type" : "chocolate", "orderDate" : ISODate("2021-03-20T11:30:05Z"),
  "state" : "WA", "price" : 14, "quantity" : 140, "rankQuantityForState" : 1 }
{ "_id" : 5, "type" : "strawberry", "orderDate" : ISODate("2019-01-08T06:12:03Z"),
  "state" : "WA", "price" : 43, "quantity" : 134, "rankQuantityForState" : 2 }
{ "_id" : 6, "type" : "strawberry", "orderDate" : ISODate("2020-01-08T06:12:03Z"),
  "state" : "WA", "price" : 41, "quantity" : 134, "rankQuantityForState" : 2 }
{ "_id" : 7, "type" : "strawberry", "orderDate" : ISODate("2020-01-01T06:12:03Z"),
  "state" : "WA", "price" : 34, "quantity" : 134, "rankQuantityForState" : 2 }
{ "_id" : 8, "type" : "strawberry", "orderDate" : ISODate("2020-01-02T06:12:03Z"),
  "state" : "WA", "price" : 40, "quantity" : 134, "rankQuantityForState" : 2 }
{ "_id" : 3, "type" : "vanilla", "orderDate" : ISODate("2020-02-08T13:13:23Z"),
  "state" : "WA", "price" : 13, "quantity" : 104, "rankQuantityForState" : 6 }

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