MongoDB聚合运算符：$setIntersection

MongoDB聚合运算符：$setIntersection

$setIntersection聚合运算符返回两个或多个数组的交集。

语法

{
   
    $setIntersection: [ <array1>, <array2>, ... ] }

字段说明：

参数可以是任何有效的数组表达式。

使用

• $setIntersection 对数组执行集合操作，将数组视为集合，如果数组包含重复元素，$setIntersection会忽略重复元素，$setIntersection忽略元素的顺序。
• $setIntersection 过滤掉结果中的重复项，输出仅包含唯一元素的数组，输出数组中元素的顺序未指定。
• 如果未找到交集（即输入数组不包含公共元素），则 $setIntersection 返回一个空数组。
• 如果集合包含嵌套数组元素，则 $setIntersection 不会下降到嵌套数组，而处理顶层数组。

例如	结果
{ $setIntersection: [ [ "a", "b", "a" ], [ "b", "a" ] ] }	[ "b", "a" ]
{ $setIntersection: [ [ "a", "b" ], [ [ "a", "b" ] ] ] }	[]

举例

元素数组举例

使用下面的脚本创建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" :