文档菜单
文档首页
/
MongoDB 手册
/
聚合操作
/
参考
/
运算符

$setUnion (聚合)

本页内容

  • 定义
  • 行为
  • 示例

定义

$setUnion

接受两个或多个数组，并返回包含任何输入数组中出现元素的数组。

$setUnion的语法如下

{ $setUnion: [ <expression1>, <expression2>, ... ] }

参数可以是任何有效的表达式，只要它们每个都解析为数组。有关表达式的更多信息，请参阅表达式运算符。

行为

$setUnion对数组执行集合操作，将数组视为集合。如果一个数组包含重复条目，$setUnion会忽略重复条目。$setUnion忽略元素的顺序。

$setUnion在其结果中过滤掉重复项，以输出只包含唯一条目的数组。输出数组中元素的顺序是不确定的。

如果一个集合包含嵌套数组元素，$setUnion不会进入嵌套数组，而是在顶层评估数组。

示例
结果
{ $setUnion: [ [ "a", "b", "a" ], [ "b", "a" ] ] }
[ "b", "a" ]
{ $setUnion: [ [ "a", "b" ], [ [ "a", "b" ] ] ] }
[ [ "a", "b" ], "b", "a" ]

注意

从MongoDB 5.2开始，$setUnion的排序顺序是不确定的。要排序数组，请参阅$sortArray。

示例

考虑一个包含以下文档的flowers集合

db.flowers.insertMany( [
   { "_id" : 1, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid" ] },
   { "_id" : 2, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "orchid", "rose", "orchid" ] },
   { "_id" : 3, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "rose", "orchid", "jasmine" ] },
   { "_id" : 4, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ "jasmine", "rose" ] },
   { "_id" : 5, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ ] },
   { "_id" : 6, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose" ], [ "orchid" ] ] },
   { "_id" : 7, "flowerFieldA" : [ "rose", "orchid" ], "flowerFieldB" : [ [ "rose", "orchid" ] ] },
   { "_id" : 8, "flowerFieldA" : [ ], "flowerFieldB" : [ ] },
   { "_id" : 9, "flowerFieldA" : [ ], "flowerFieldB" : [ "rose" ] }
] )

以下操作使用 $setUnion 运算符来返回在 flowerFieldA 数组或 flowerFieldB 数组中或两个数组中都存在的元素组成的数组。

db.flowers.aggregate(
   [
     { $project: { flowerFieldA:1, flowerFieldB: 1, allValues: { $setUnion: [ "$flowerFieldA", "$flowerFieldB" ] }, _id: 0 } }
   ]
)

操作返回以下结果

{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "rose", "orchid" ], "allValues": [ "orchid", "rose" ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "orchid", "rose", "orchid" ], "allValues": [ "orchid", "rose" ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "rose", "orchid", "jasmine" ], "allValues": [ "orchid", "rose", "jasmine" ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ "jasmine", "rose" ], "allValues": [ "orchid", "rose", "jasmine" ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ ], "allValues": [ "orchid", "rose" ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ [ "rose" ], [ "orchid" ] ], "allValues": [ "orchid", "rose", [ "rose" ], [ "orchid" ] ] }
{ "flowerFieldA": [ "rose", "orchid" ], "flowerFieldB": [ [ "rose", "orchid" ] ], "allValues": [ "orchid", "rose", [ "rose", "orchid" ] ] }
{ "flowerFieldA": [ ], "flowerFieldB": [ ], "allValues": [ ] }
{ "flowerFieldA": [ ], "flowerFieldB": [ "rose" ], "allValues": [ "rose" ] }

返回

集合是否为子集

下一步

shift

本页内容