使用 $match 的聚合查询在 MongoDB 中有效吗?
mongodbdatabasebig data analytics更新于 2026/1/9 16:37:17
是的，它在 MongoDB 中有效。让我们创建一个包含文档的集合。 −
> db.demo358.insertOne({"ClientId":101,"ClientName":"Chris","ClientAge":34});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5692c0f8647eb59e5620cb")
}
> db.demo358.insertOne({"ClientId":102,"ClientName":"David","ClientAge":32});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5692caf8647eb59e5620cc")
}
> db.demo358.insertOne({"ClientId":103,"ClientName":"David","ClientAge":35});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5692d2f8647eb59e5620cd")
}
> db.demo358.insertOne({"ClientId":104,"ClientName":"Bob","ClientAge":31});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5692ddf8647eb59e5620ce")
}
> db.demo358.insertOne({"ClientId":105,"ClientName":"Chris","ClientAge":36});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5692e7f8647eb59e5620cf")
}
借助 find() 方法显示集合中的所有文档 −
> db.demo358.find();
这将产生以下输出 −
{ "_id" : ObjectId("5e5692c0f8647eb59e5620cb"), "ClientId" : 101, "ClientName" : "Chris", "ClientAge" : 34 }
{ "_id" : ObjectId("5e5692caf8647eb59e5620cc"), "ClientId" : 102, "ClientName" : "David", "ClientAge" : 32 }
{ "_id" : ObjectId("5e5692d2f8647eb59e5620cd"), "ClientId" : 103, "ClientName" : "David", "ClientAge" : 35 }
{ "_id" : ObjectId("5e5692ddf8647eb59e5620ce"), "ClientId" : 104, "ClientName" : "Bob", "ClientAge" : 31 }
{ "_id" : ObjectId("5e5692e7f8647eb59e5620cf"), "ClientId" : 105, "ClientName" : "Chris", "ClientAge" : 36 }
以下是如何在聚合中使用 $match−
> db.demo358.aggregate(
... [ { $match : { "ClientName" : "David" }},
... { "$count": "ClientName" }
... ]
... );
这将产生以下输出 −
{ "ClientName" : 2 }
