MongoDB查询是否使用聚合框架将多个字段分组？
要对多个字段进行分组，请在MongoDB中使用$group。让我们创建一个包含文档的集合-
> db.demo192.insertOne({"Name":"Chris","Age":22});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3adb9f03d395bdc21346cd")
}
> db.demo192.insertOne({"Name":"David","Age":21});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3adba103d395bdc21346ce")
}
> db.demo192.insertOne({"Name":"Chris","Age":22});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3adba503d395bdc21346cf")
}
> db.demo192.insertOne({"Name":"Mike","Age":24});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3adbbf03d395bdc21346d0")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo192.find();
这将产生以下输出-
{ "_id" : ObjectId("5e3adb9f03d395bdc21346cd"), "Name" : "Chris", "Age" : 22 }
{ "_id" : ObjectId("5e3adba103d395bdc21346ce"), "Name" : "David", "Age" : 21 }
{ "_id" : ObjectId("5e3adba503d395bdc21346cf"), "Name" : "Chris", "Age" : 22 }
{ "_id" : ObjectId("5e3adbbf03d395bdc21346d0"), "Name" : "Mike", "Age" : 24 }以下是使用聚合框架对几个字段进行分组的查询-
> db.demo192.aggregate([{$group:{_id:{Age:"$Age",Name:"$Name"}}}]);这将产生以下输出-
{ "_id" : { "Age" : 24, "Name" : "Mike" } }
{ "_id" : { "Age" : 21, "Name" : "David" } }
{ "_id" : { "Age" : 22, "Name" : "Chris" } }