获取聚合的MongoDB中的平均分数？
将$avg运算符与聚合框架一起使用。首先让我们创建一个包含文档的集合。在这里，字段之一是StudentScore-
> db.averageReturiningNullDemo.insertOne(
{"StudentDetails" : { "StudentScore" : 89 }
});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ce9822e78f00858fb12e927")
}
> db.averageReturiningNullDemo.insertOne(
{"StudentDetails" : { "StudentScore" : 34 }
});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ce9822e78f00858fb12e928")
}
> db.averageReturiningNullDemo.insertOne(
{"StudentDetails" : { "StudentScore" : 78 }
});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ce9822e78f00858fb12e929")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.averageReturiningNullDemo.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5ce9822e78f00858fb12e927"),
"StudentDetails" : {
"StudentScore" : 89
}
}
{
"_id" : ObjectId("5ce9822e78f00858fb12e928"),
"StudentDetails" : {
"StudentScore" : 34
}
}
{
"_id" : ObjectId("5ce9822e78f00858fb12e929"),
"StudentDetails" : {
"StudentScore" : 78
}
}以下是对平均回报的查询-
> db.averageReturiningNullDemo.aggregate([
{
"$group": {
"_id": null,
"StudentScoreAverage": {
"$avg": "$StudentDetails.StudentScore"
}
}
}
]);这将产生以下输出-
{ "_id" : null, "StudentScoreAverage" : 67 }