MongoDB查询将重复的文档分组
aggregate()。让我们创建一个包含文档的集合-> db.demo501.insertOne({"Name":"Chris"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8752f0987b6e0e9d18f566")
}
> db.demo501.insertOne({"Name":"Bob"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8752f4987b6e0e9d18f567")
}
> db.demo501.insertOne({"Name":"Chris"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8752f8987b6e0e9d18f568")
}
> db.demo501.insertOne({"Name":"John"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8752fb987b6e0e9d18f569")
}
> db.demo501.insertOne({"Name":"Chris"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8752fd987b6e0e9d18f56a")
}
> db.demo501.insertOne({"Name":"John"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e875301987b6e0e9d18f56b")
}
> db.demo501.insertOne({"Name":"David"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e875307987b6e0e9d18f56c")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo501.find();
这将产生以下输出-
{ "_id" : ObjectId("5e8752f0987b6e0e9d18f566"), "Name" : "Chris" }
{ "_id" : ObjectId("5e8752f4987b6e0e9d18f567"), "Name" : "Bob" }
{ "_id" : ObjectId("5e8752f8987b6e0e9d18f568"), "Name" : "Chris" }
{ "_id" : ObjectId("5e8752fb987b6e0e9d18f569"), "Name" : "John" }
{ "_id" : ObjectId("5e8752fd987b6e0e9d18f56a"), "Name" : "Chris" }
{ "_id" : ObjectId("5e875301987b6e0e9d18f56b"), "Name" : "John" }
{ "_id" : ObjectId("5e875307987b6e0e9d18f56c"), "Name" : "David" }以下是对MongoDB中重复文档进行分组的查询-
> db.demo501.aggregate( [ { $group : { _id : "$Name" } } ] )这将产生以下输出-
{ "_id" : "David" }
{ "_id" : "John" }
{ "_id" : "Bob" }
{ "_id" : "Chris" }