数据结构
网络
RDBMS
操作系统
Java
MS Excel
iOS
HTML
CSS
Android
Python
C 编程
C++
C#
MongoDB
MySQL
Javascript
PHP
物理
化学
生物
数学
英语
经济
心理学
社会学
时尚研究
法律研究MongoDB 查询以实现聚合函数
我们首先使用文档创建集合 -
> db.demo121.insertOne(
... {
... "Id" : 101,
... "Details" : [
... {
... "SubjectId" : "1",
... "SubjectName" : "MongoDB",
... "Score" : 76
... },
... {
... "SubjectId" : "2",
... "SubjectName" : "MySQL",
... "Score" : 76
... },
... {
... "SubjectId" : "3",
... "SubjectName" : "Java",
... "Score" : 76
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2f1c60140daf4c2a3544b3")
}使用 find() 方法从集合中显示所有文档 -
> db.demo121.find();
这将产生以下输出 -
{
"_id" : ObjectId("5e2f1c60140daf4c2a3544b3"), "Id" : 101, "Details" : [
{ "SubjectId" : "1", "SubjectName" : "MongoDB", "Score" : 76 },
{ "SubjectId" : "2", "SubjectName" : "MySQL", "Score" : 76 },
{ "SubjectId" : "3", "SubjectName" : "Java", "Score" : 76 }
]
}以下是实现聚合函数的查询 -
> db.demo121.aggregate([
... { "$match": { "Id": 101 } },
... { "$unwind": "$Details" },
... {
... "$group": {
... "_id": "$Details.SubjectId",
... "count": { "$sum": 1 },
... "Details": {
... "$push": {
... "SubjectName": "$Details.SubjectName"
... }
... }
... }
... },
... {
... "$group": {
... "_id": null,
... "List": {
... "$push": {
... "SubId": "$_id",
... "Details": "$Details"
... }
... }
... }
... }
... ], function (err, out) {
... res.json(out);
... });这将产生以下输出 -
{
"_id" : null, "List" : [
{ "SubId" : "3", "Details" : [ { "SubjectName" : "Java" } ] },
{ "SubId" : "2", "Details" : [ { "SubjectName" : "MySQL" } ] },
{ "SubId" : "1", "Details" : [ { "SubjectName" : "MongoDB" } ] }
]
}
更新于：2020 年 3 月 31 日
156 次浏览
广告