快速获取MongoDB中特定值的计数
为了更快地查询，请创建一个索引。要获取计数，请使用count()。让我们创建一个包含文档的集合-
> db.demo311.ensureIndex({"Name":1});
{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.demo311.insertOne({"Name":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e50cd01f8647eb59e562044")
}
> db.demo311.insertOne({"Name":"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e50cd05f8647eb59e562045")
}
> db.demo311.insertOne({"Name":"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e50cd06f8647eb59e562046")
}
> db.demo311.insertOne({"Name":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e50cd0af8647eb59e562047")
}
> db.demo311.insertOne({"Name":"Bob"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e50cd0df8647eb59e562048")
}
> db.demo311.insertOne({"Name":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e50cd0ff8647eb59e562049")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo311.find();
这将产生以下输出-
{ "_id" : ObjectId("5e50cd01f8647eb59e562044"), "Name" : "Chris" }
{ "_id" : ObjectId("5e50cd05f8647eb59e562045"), "Name" : "David" }
{ "_id" : ObjectId("5e50cd06f8647eb59e562046"), "Name" : "David" }
{ "_id" : ObjectId("5e50cd0af8647eb59e562047"), "Name" : "Chris" }
{ "_id" : ObjectId("5e50cd0df8647eb59e562048"), "Name" : "Bob" }
{ "_id" : ObjectId("5e50cd0ff8647eb59e562049"), "Name" : "Chris" }以下是获取特定值的计数的查询-
> db.demo311.find({"Name":"Chris"}).count();这将产生以下输出-
3