快速获取 MongoDB 中特定值的计数
mongodbdatabasebig data analytics更新于 2026/1/10 4:22:17
为了加快查询速度，请创建索引。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")
}
借助 find() 方法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" }
以下是获取特定值计数的查询 −
> db.demo311.find({"Name":"Chris"}).count();
这将产生以下输出 −
3
