为此，请使用 aggregate() 以及 $filter。让我们创建一个包含文档的集合 −> db.demo137.insertOne( ... { ... Name1:"Chris", ... Name2:"David", ... Detail1:[ ... {_id:"John", Name3:"Chris"}, ... {_id:"Chris", Name3:"Chris"}, ... ], ... Detail2:[{_id:"David", Name3:"Chris"}, ... {_id:"Carol", Name3:"Chris"}, ... {_id:"John", Name3:"Chris"}] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5e31b4cefdf09dd6d08539a0") }使用 find() 方法显示集合中的所有文档 −> db.demo137.find();这将… 阅读更多

让我们创建一个包含文档的集合 −> db.demo136.insertOne( ... { ... "Name":"Chris", ... "Details":[ ... { ... "Id":"101", ... "EmployeeName":"Mike", ... "EmployeeDetails":[ ... { ... "EmpId":1001, ... "Salary":1000 ... }, ... { ... ... 阅读更多

要更新，请使用 $set 以及 UPDATE。让我们创建一个包含文档的集合 −>db.demo135.insertOne({"Details":[{"EmployeeId":101, "EmployeeName":"Chris", "EmployeeSalary":45000}, {"EmployeeId":102, "EmployeeName":"Chris", "EmployeeSalary":45000}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e31a5ddfdf09dd6d085399c") }使用 find() 方法显示集合中的所有文档 −> db.demo135.find().pretty();这将产生以下输出 −{ "_id" : ObjectId("5e31a5ddfdf09dd6d085399c"), "Details" : [ { "EmployeeId" : 101, "EmployeeName" : "Chris", "EmployeeSalary" : 45000 }, { "EmployeeId" : 102, ... 阅读更多

要更新，请使用 update() 以及 $set。让我们创建一个包含文档的集合 −>db.demo134.insertOne({"EmployeeId":101, "EmployeeDetails":[{"EmployeeName":"Chris", "EmployeeAge":27}, {"EmployeeName":"Bob", "EmployeeAge":28}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e319b2f68e7f832db1a7f7c") } >db.demo134.insertOne({"EmployeeId":102, "EmployeeDetails":[{"EmployeeName":"David", "EmployeeAge":24}, {"EmployeeName":"Carol", "EmployeeAge":29}]}); { "acknowledged" : true, "insertedId" : ObjectId("5e319b4468e7f832db1a7f7d") }使用 find() 方法显示集合中的所有文档 −> db.demo134.find().pretty();这将产生以下输出 −{ "_id" : ObjectId("5e319b2f68e7f832db1a7f7c"), "EmployeeId" : 101, "EmployeeDetails" : [ { "EmployeeName" : "Chris", "EmployeeAge" : 27 }, ... 阅读更多

要分组，请在 MongoDB 中使用 $week 和 $month。让我们创建一个包含文档的集合 −> db.demo133.insertOne({"Rank":18, "DueDate":new ISODate("2020-01-10")}); { "acknowledged" : true, "insertedId" : ObjectId("5e31980968e7f832db1a7f78") } > db.demo133.insertOne({"Rank":12, "DueDate":new ISODate("2020-01-10")}); { "acknowledged" : true, "insertedId" : ObjectId("5e31982568e7f832db1a7f79") } > db.demo133.insertOne({"Rank":12, "DueDate":new ISODate("2020-02-01")}); { "acknowledged" : true, "insertedId" : ObjectId("5e31986568e7f832db1a7f7a") } > db.demo133.insertOne({"Rank":20, "DueDate":new ISODate("2020-02-01")}); { "acknowledged" : true, "insertedId" : ObjectId("5e31986c68e7f832db1a7f7b") }使用 find() 方法显示集合中的所有文档 −> db.demo133.find();这将产生以下输出 −{ "_id" : ObjectId("5e31980968e7f832db1a7f78"), "Rank" : 18, "DueDate" : ISODate("2020-01-10T00:00:00Z") } ... 阅读更多

要跨两列分组，请使用 $lookup。让我们创建一个包含文档的集合 −> db.demo132.insertOne({"CountryName1":"US", "CountryName2":"UK", Value:50}); { "acknowledged" : true, "insertedId" : ObjectId("5e31950468e7f832db1a7f75") } > db.demo132.insertOne({"CountryName1":"UK", "CountryName2":"AUS", Value:10}); { "acknowledged" : true, "insertedId" : ObjectId("5e31951d68e7f832db1a7f76") } > db.demo132.insertOne({"CountryName1":"AUS", "CountryName2":"US", Value:40}); { "acknowledged" : true, "insertedId" : ObjectId("5e31952c68e7f832db1a7f77") }使用 find() 方法显示集合中的所有文档 −> db.demo132.find();这将产生以下输出 −{ "_id" : ObjectId("5e31950468e7f832db1a7f75"), "CountryName1" : "US", "CountryName2" : "UK", "Value" : 50 } { "_id" : ObjectId("5e31951d68e7f832db1a7f76"), "CountryName1" : "UK", "CountryName2" : "AUS", "Value" : ... 阅读更多

为此，请在 MongoDB 中使用 aggregate()。让我们首先创建一个包含文档的集合 −> db.demo131.insertOne( ... { ... "_id": 101, ... "Details": [ ... { ... "PlayerScore": 500, ... "PlayerName": "Chris" ... }, ... { ... "PlayerScore": 400, ... "PlayerName": "David" ... } ... ] ... } ... ... 阅读更多

让我们首先创建一个包含文档的集合 −> db.demo130.insertOne( ... { ... "PlayerDetails":[{Score:56}, {Score:78}, {Score:89}, {Score:97}] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5e3065bf68e7f832db1a7f6d") } > db.demo130.insertOne( ... { ... "PlayerDetails":[{Score:45}, {Score:56}] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5e3065c068e7f832db1a7f6e") }使用 find() 方法显示集合中的所有文档 −> db.demo130.find();这将产生以下输出 −{ "_id" : ObjectId("5e3065bf68e7f832db1a7f6d"), "PlayerDetails" : [ { "Score" : 56 }, { "Score" : 78 }, { "Score" : 89 }, ... 阅读更多

要获取字符串中不同的首个单词，请使用 split()。让我们首先创建一个包含文档的集合 −> db.demo129.insertOne({"Words":"This is the MySQL", "CountryName":"US"}); { "acknowledged" : true, "insertedId" : ObjectId("5e305d6368e7f832db1a7f6b") } > db.demo129.insertOne({"Words":"MongoDB is NOSQL database", "CountryName":"US"}); { "acknowledged" : true, "insertedId" : ObjectId("5e305d7b68e7f832db1a7f6c") }使用 find() 方法显示集合中的所有文档 −> db.demo129.find();这将产生以下输出 −{ "_id" : ObjectId("5e305d6368e7f832db1a7f6b"), "Words" : "This is the MySQL", "CountryName" : "US" } { "_id" : ObjectId("5e305d7b68e7f832db1a7f6c"), "Words" : "MongoDB is NOSQL database", "CountryName" : "US" }以下是如何… 阅读更多

要在MongoDB中获取列的唯一值，可以使用distinct()方法。让我们先创建一个包含文档的集合：-> db.demo128.insertOne({"Name":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e30583d68e7f832db1a7f5d") } > db.demo128.insertOne({"Name":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e30584068e7f832db1a7f5e") } > db.demo128.insertOne({"Name":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e30584368e7f832db1a7f5f") } > db.demo128.insertOne({"Name":"Bob"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e30584668e7f832db1a7f60") } > db.demo128.insertOne({"Name":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e30584c68e7f832db1a7f61") } 使用find()方法显示集合中的所有文档 -> db.demo128.find(); 这将产生以下输出：{ "_id" : ... 阅读更多