MongoDB查询以计算平均值
要计算MongoDB中的平均值，请使用$avg。让我们创建一个包含文档的集合-
> db.demo80.insertOne({"Details":{"Price":10.5}});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bf43271bf0181ecc42297")
}
> db.demo80.insertOne({"Details":{"Price":50.3}});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bf43871bf0181ecc42298")
}
> db.demo80.insertOne({"Details":{"Price":100.10}});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2bf43f71bf0181ecc42299")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo80.find();
这将产生以下输出-
{ "_id" : ObjectId("5e2bf43271bf0181ecc42297"), "Details" : { "Price" : 10.5 } }
{ "_id" : ObjectId("5e2bf43871bf0181ecc42298"), "Details" : { "Price" : 50.3 } }
{ "_id" : ObjectId("5e2bf43f71bf0181ecc42299"), "Details" : { "Price" : 100.1 } }以下是在MongoDB中获取平均值的查询-
> db.demo80.aggregate([
... {
... "$group": {
... "_id": null,
... "AvgValue": {
... "$avg": "$Details.Price"
... }
... }
... }
... ]);这将产生以下输出-
{ "_id" : null, "AvgValue" : 53.633333333333326 }