如何使用 MongoDB $group 获取值列表?
mongodbdatabasebig data analytics更新于 2026/1/14 4:07:17
要获取值列表，请使用 $group 聚合和 $push 运算符。首先，我们创建一个包含文档的集合。 −
> db.groupByDemo.insertOne({"UserName":"John","Subject":"MongoDB"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd69f0457806ebf1256f136")
}
> db.groupByDemo.insertOne({"UserName":"Larry","Subject":"MySQL"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd69f0657806ebf1256f137")
}
> db.groupByDemo.insertOne({"UserName":"John","Subject":"Java"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd69f0d57806ebf1256f138")
}
> db.groupByDemo.insertOne({"UserName":"John","Subject":"C"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd69f1357806ebf1256f139")
}
> db.groupByDemo.insertOne({"UserName":"Larry","Subject":"SQL Server"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd69f1c57806ebf1256f13a")
}
以下是使用 find() 方法显示集合中的所有文档的查询 −
> db.groupByDemo.find().pretty();
这将产生以下输出 −
{
"_id" : ObjectId("5cd69f0457806ebf1256f136"),
"UserName" : "John",
"Subject" : "MongoDB"
}
{
"_id" : ObjectId("5cd69f0657806ebf1256f137"),
"UserName" : "Larry",
"Subject" : "MySQL"
}
{
"_id" : ObjectId("5cd69f0d57806ebf1256f138"),
"UserName" : "John",
"Subject" : "Java"
}
{
"_id" : ObjectId("5cd69f1357806ebf1256f139"),
"UserName" : "John",
"Subject" : "C"
}
{
"_id" : ObjectId("5cd69f1c57806ebf1256f13a"),
"UserName" : "Larry",
"Subject" : "SQL Server"
}
以下是使用 $group 和 $push 获取值列表的查询 −
> db.groupByDemo.aggregate({$group: { '_id': '$UserName', 'Subject': { $push: '$Subject'}}});
这将产生以下输出 −
{ "_id" : "Larry", "Subject" : [ "MySQL", "SQL Server" ] }
{ "_id" : "John", "Subject" : [ "MongoDB", "Java", "C" ] }
