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MongoDB Group（分組）

 $group 依指定屬性分組資料 // prepare data> db.company.insertOne({"name":"A","foundYear":1980,"numberOfEmployee":50}){ "acknowledged" : true, "i...

MongoDB Compound Index

At first, schema in mongodb is as follows > db.users.find() { "_id" : ObjectId("5f6f162c432d41b06263640d"), "name" : "user12", "i" : 12, "age" : 27, "cre...

MongoDB 複合索引

首先，MongoDB 中的 schema 如下 > db.users.find() { "_id" : ObjectId("5f6f162c432d41b06263640d"), "name" : "user12", "i" : 12, "age" : 27, "createdAt" : ISODate(...

MongoDB Index

 explain is used to understand execution detail In this case,"totalDocsExamined" : 1380558: shows "query by username" is quite insufficient db.users.fin...

MongoDB 索引

 explain 用來了解執行細節 在這個例子中，"totalDocsExamined" : 1380558：顯示「用 username 查詢」效率非常差 db.users.find({"username": "user101"}).explain("executionStats")> db.us...

Query MongoDB

  <div>specify returned attributes</div><div><div>// find all with all attributes</div><div>> db.users.find().pre...

查詢 MongoDB

  <div>指定回傳的屬性</div><div><div>// find all with all attributes</div><div>> db.users.find().pretty()</div><...