MongoDB聚合以获取相应重复名称的字段值的计数？
让我们看一个示例并创建包含文档的集合-
> db.demo558.insertOne(
... {
... _id : 100,
... CountryCode:101,
... details: [
... {
... Name:"Chris",
... Subject:"MySQL"
... },
... {
... Name:"Chris",
... Subject:"MongoDB"
... },
... {
... Name:"Chris",
... Subject:"Java"
... },
... {
... Name:"Bob",
... Subject:"Python"
... },
... {
... Name:"Bob",
... Subject:"Java"
... }
... ]
... }
... )
{ "acknowledged" : true, "insertedId" : 100 }在find()方法的帮助下显示集合中的所有文档-
> db.demo558.find();
这将产生以下输出-
{ "_id" : 100, "CountryCode" : 101, "details" : [
{ "Name" : "Chris", "Subject" : "MySQL" },
{ "Name" : "Chris", "Subject" : "MongoDB" },
{ "Name" : "Chris", "Subject" : "Java" },
{ "Name" : "Bob", "Subject" : "Python" },
{ "Name" : "Bob", "Subject" : "Java" }
] }以下是获取计数的查询-
> db.demo558.aggregate([
... {$unwind: "$details" },
... {$group: { _id: "$details.Name", NameCount:{$sum : 1}, Subject : {$push: "$details.Subject"}}},
... {$project: { NameCount: 1, SubjectCount : {$size: "$Subject"}}}
... ]).pretty()这将产生以下输出-
{ "_id" : "Bob", "NameCount" : 2, "SubjectCount" : 2 }
{ "_id" : "Chris", "NameCount" : 3, "SubjectCount" : 3 }