如何在MongoDB聚合中将数组元素的子集相加？
> db.demo610.insertOne({Values:[10,20,30,40,50]});{
"acknowledged" : true, "insertedId" : ObjectId("5e9747b8f57d0dc0b182d62e")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo610.find().pretty()
这将产生以下输出-
{
"_id" : ObjectId("5e9747b8f57d0dc0b182d62e"),
"Values" : [
10,
20,
30,
40,
50
]
}这是将MongoDB聚合中数组元素的子集加在一起的查询-
> db.demo610.aggregate([
... {$unwind:"$Values"},
... {$group:{"_id":"$_id",
... "1st":{$first:"$Values"},
... "All":{$sum:"$Values"}}},
... {$project:{"_id":"$_id",
... "SumOfAllMinus1":{$subtract:["$All","$1st"]}}},
... {$group:{"_id":null,
... "SumOfAllExcept1stValue":{$sum:"$SumOfAllMinus1"}}}
... ])这将产生以下输出-
{ "_id" : null, "SumOfAllExcept1stValue" : 140 }