如何计算 MongoDB 文档中按 null 分组的平均值?
mongodbdatabasebig data analytics更新于 2026/1/15 10:07:17
您可以使用 $group 运算符，并将 _id: null 设置为 null。语法如下:−
db.yourCollectionName.aggregate([{$group: {_id:null, "anyFieldName": {$avg:"$yourFieldName"} } }]);
首先，我们创建一个包含文档的集合 −
> db.caculateTheAverageValueDemo.insertOne({"Population":100});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd68a197924bb85b3f4895f")
}
> db.caculateTheAverageValueDemo.insertOne({"Population":500});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd68a1c7924bb85b3f48960")
}
> db.caculateTheAverageValueDemo.insertOne({"Population":200});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd68a237924bb85b3f48961")
}
> db.caculateTheAverageValueDemo.insertOne({"Population":100});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd68a297924bb85b3f48962")
}
> db.caculateTheAverageValueDemo.insertOne({"Population":100});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd68a2e7924bb85b3f48963")
}
以下是使用 find() 方法显示集合中的所有文档的查询 −
> db.caculateTheAverageValueDemo.find().pretty();
这将产生以下输出 −
{ "_id" : ObjectId("5cd68a197924bb85b3f4895f"), "Population" : 100 }
{ "_id" : ObjectId("5cd68a1c7924bb85b3f48960"), "Population" : 500 }
{ "_id" : ObjectId("5cd68a237924bb85b3f48961"), "Population" : 200 }
{ "_id" : ObjectId("5cd68a297924bb85b3f48962"), "Population" : 100 }
{ "_id" : ObjectId("5cd68a2e7924bb85b3f48963"), "Population" : 100 }
以下是用于对 MongoDB 文档的值进行平均的查询 −
> db.caculateTheAverageValueDemo.aggregate([{$group: {_id:null, "AveragePopulation": {$avg:"$Population"} } }]);
这将产生以下输出 −
{ "_id" : null, "AveragePopulation" : 200 }
