如何在MongoDB中汇总总和以获得总数？
要在MongoDB中汇总总和以获取总计数，可以使用$sum运算符。要了解上述概念，让我们使用文档创建一个集合-
> db.aggregateSumDemo.insertOne({"CustomerName":"Larry","Amount":140});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8baa0680f10143d8431e18")
}
> db.aggregateSumDemo.insertOne({"CustomerName":"Mike","Amount":160});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8baa1380f10143d8431e19")
}
> db.aggregateSumDemo.insertOne({"CustomerName":"Sam","Amount":300});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8baa1c80f10143d8431e1a")
}
> db.aggregateSumDemo.insertOne({"CustomerName":"David","Amount":500});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8baa2580f10143d8431e1b")
}在find()method的帮助下显示集合中的所有文档。查询如下-
> db.aggregateSumDemo.find().pretty();
以下是输出-
{
"_id" : ObjectId("5c8baa0680f10143d8431e18"),
"CustomerName" : "Larry",
"Amount" : 140
}
{
"_id" : ObjectId("5c8baa1380f10143d8431e19"),
"CustomerName" : "Mike",
"Amount" : 160
}
{
"_id" : ObjectId("5c8baa1c80f10143d8431e1a"),
"CustomerName" : "Sam",
"Amount" : 300
}
{
"_id" : ObjectId("5c8baa2580f10143d8431e1b"),
"CustomerName" : "David",
"Amount" : 500
}这是获取总数的查询。
情况1-查询如下-
> db.aggregateSumDemo.aggregate([ {
... $group: {
... _id: null,
... "TotalCount": {
... $sum:1
... }
... }
... } ] );以下是输出-
{ "_id" : null, "TotalCount" : 4 }这是在MongoDB中汇总总和以获取总和的查询。
情况2-查询如下-
> db.aggregateSumDemo.aggregate([ {
... $group: {
... _id: null,
... "TotalAmount": {
... $sum: "$Amount"
... }
... }
... } ] );以下是输出-
{ "_id" : null, "TotalAmount" : 1100 }