定义
版本 5.0 中的新增功能。
返回文档在 $setWindowFields阶段分区中相对于其他文档的位置（称为排名）。
$setWindowFields 阶段中的 sortBy 字段值决定了文档排名。与 $rank 操作符一起使用时，sortBy 只能将一个字段作为其值。有关 MongoDB 如何比较不同类型字段的更多信息，请参阅 BSON 比较顺序。
如果多个文档占据相同的秩，$rank 会将具有后续值的文档放在有差异的秩上（请参阅行为）。
$rank 只能在 $setWindowFields 阶段使用。
$rank 事务语法：
{ $rank: { } }
$rank 不接受任何参数。
行为
$rank 和 $denseRank 在如何排列重复的 sortBy 字段值方面有所不同。例如，sortBy 字段值为 7、9、9 和 10：
$denseRank对这些值排列名次，为 1、2、2 和 3。重复的 9 个值的排名为 2，重复的 10 个值的排名为 3。这些排名没有差异。$rank对这些值排列名次，为 1、2、2 和 4。重复的 9 个值的排名为 2，而 10 的排名为 4。排名 3 存在差异。
sortBy 字段值为 null 的文档或缺少 sortBy 字段的文档根据 BSON 比较顺序分配排名。
请参阅对包含重复值、空值或缺失数据的分区进行排名中的示例。
示例
创建cakeSales集合，其中包含加利福尼亚州 ( CA ) 和华盛顿州 ( WA ) 的蛋糕销售情况：
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 } ] )
按整数字段对分区排序
此示例在 $setWindowFields 阶段使用 $rank，针对每个 state 输出蛋糕销售 quantity 的排名：
db.cakeSales.aggregate( [ { $setWindowFields: { partitionBy: "$state", sortBy: { quantity: -1 }, output: { rankQuantityForState: { $rank: {} } } } } ] )
在示例中：
partitionBy: "$state"按state对集合中的文档分区。CA和WA都有分区。sortBy: { quantity: -1 }按quantity以降序 (-1) 对每个分区中的文档进行排序，因此最高的quantity位于最前面。
output使用$rank将rankQuantityForState字段设置为quantity排名，如以下结果所示。
{ "_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 $setWindowFields 阶段使用日期和 $rank 来输出每个 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"按state对集合中的文档分区。CA和WA都有分区。sortBy: { orderDate: 1 }按orderDate以升序 (1) 对每个分区中的文档进行排序，因此最早的orderDate位于最前面。
output使用$rank将rankOrderDateForState字段设置为orderDate排名，如以下结果所示。
{ "_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 }
对包含重复值、空值或缺失数据的分区进行排名
创建 cakeSalesWithDuplicates 集合，其中：
蛋糕销售位于加利福尼亚州 (
CA) 和华盛顿州 (WA)。文档 6 至 8 与文档 5 具有相同的
quantity和state。文档 9 具有与文档 4 相同的
quantity和state。文档 10 包含
nullquantity。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 } ] )
该示例在 $setWindowFields 阶段使用 $rank，以从 cakeSalesWithDuplicates 集合中输出每个 state 的 quantity 排名：
db.cakeSalesWithDuplicates.aggregate( [ { $setWindowFields: { partitionBy: "$state", sortBy: { quantity: -1 }, output: { rankQuantityForState: { $rank: {} } } } } ] )
在示例中：
partitionBy: "$state"按state对集合中的文档分区。CA和WA都有分区。sortBy: { quantity: -1 }按quantity以降序 (-1) 对每个分区中的文档进行排序，因此最高的quantity位于最前面。
在以下示例输出中：
具有相同
quantity和state的文档具有相同的排名。如果多份文档排名相同，则该排名与下个排名之间存在差距。包含
nullquantity的文档以及缺失quantity的文档在CA分区的输出中排名最低。这种排序是按照 BSON 比较顺序分配排名的结果，在本示例中，BSON 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" : 6 } { "_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 }