MongoDB聚合从文档和数组元素获取平均值
为此，请使用$avg以及$group和aggregate()。让我们创建一个包含文档的集合-
> db.demo598.insertOne(
... {
... Information:'Student',
... id:100,
... details:[
... {Name:'Chris',Marks:75},
... {Name:'Bob',Marks:55}
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e947fccf5f1e70e134e2694")
}
> db.demo598.insertOne(
... {
... Information:'Student',
... id:101,
... details:[
... {Name:'Chris',Marks:75},
... {Name:'Bob',Marks:45}
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e947fcdf5f1e70e134e2695")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo598.find();
这将产生以下输出-
{ "_id" : ObjectId("5e947fccf5f1e70e134e2694"), "Information" : "Student", "id" : 100, "details" : [
{ "Name" : "Chris", "Marks" : 75 },
{ "Name" : "Bob", "Marks" : 55 }
] }
{ "_id" : ObjectId("5e947fcdf5f1e70e134e2695"), "Information" : "Student", "id" : 101, "details" : [
{ "Name" : "Chris", "Marks" : 75 },
{ "Name" : "Bob", "Marks" : 45 }
] }以下是从文档和数组元素获取平均值的查询-
> db.demo598.aggregate([
...
... { "$group": {
... "_id": "Information",
... "id": { "$avg": "$id" },
... "details": { "$push": "$details" }
... }},
... { "$unwind": "$details" },
... { "$unwind": "$details" },
... { "$group": {
... "_id": { "Information": "$_id", "Name": "$details.Name" },
... "id": { "$avg": "$id" },
... "AvgValue": { "$avg": "$details.Marks" }
... }},
... { "$sort": { "_id": 1 } },
... { "$group": {
... "_id": "$_id.Information",
... "id": { "$avg": "$id" },
... "details": { "$push": {
... "Name": "$_id.Name",
... "MarksAvg": "$AvgValue"
... }}
... }}
... ]).pretty();这将产生以下输出-
{
"_id" : "Information",
"id" : 100.5,
"details" : [
{
"Name" : "Bob",
"MarksAvg" : 50
},
{
"Name" : "Chris",
"MarksAvg" : 75
}
]
}