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Found 6702 Articles for Database
![Nishtha Thakur](https://www.tutorialspoint.com/assets/profiles/13598/profile/60_104893-1512719058.jpg)
1K+ Views
To remove key fields in MongoFB, you can use $unset operator. Let us first create a collection with documents −>db.removeKeyFieldsDemo.insertOne({"StudentFirstName":"John", "StudentLastName":"Doe", "StudentAge":23}); { "acknowledged" : true, "insertedId" : ObjectId("5cc6c8289cb58ca2b005e672") } >db.removeKeyFieldsDemo.insertOne({"StudentFirstName":"John", "StudentLastName":"Smith", "StudentAge":21}); { "acknowledged" : true, "insertedId" : ObjectId("5cc6c8359cb58ca2b005e673") }Following is the query to display all documents from a collection with the help of find() method −> db.removeKeyFieldsDemo.find().pretty();This will produce the following output −{ "_id" : ObjectId("5cc6c8289cb58ca2b005e672"), "StudentFirstName" : "John", "StudentLastName" : "Doe", "StudentAge" : 23 } { "_id" : ObjectId("5cc6c8359cb58ca2b005e673"), "StudentFirstName" : "John", "StudentLastName" : "Smith", ... Read More
![Smita Kapse](https://www.tutorialspoint.com/assets/profiles/13597/profile/60_103706-1512718957.jpg)
251 Views
You can use the concept of map reduce to get the position in an array. Let us first create a collection with documents −> db.retrievePositionDemo.find(); { "_id" : ObjectId("5cd569ec7924bb85b3f4893f"), "Subjects" : [ "MySQL", "MongoDB", "Java" ] }Following is the query to display all documents from a collection with the help of find() method −> db.retrievePositionDemo.find().pretty();This will produce the following output −{ "_id" : ObjectId("5cd569ec7924bb85b3f4893f"), "Subjects" : [ "MySQL", "MongoDB", "Java" ] }Following is the query to retrieve the position in an array in MongoDB ... Read More
![Anvi Jain](https://www.tutorialspoint.com/assets/profiles/13591/profile/60_98631-1512716973.jpg)
525 Views
For MongoDB multidimensional array projection, you need to use aggregate framework. Let us first create a collection with documents. Here, we have multidimensional array for Student marks −> db.multiDimensionalArrayProjection.insertOne( ... { ... "StudentFirstName" : "Chris", ... "StudentMarks" : [ [98, 99], [56, 79] ] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5cc6b75a9cb58ca2b005e66c") }Following is the query to display all documents from a collection with the help of find() method −> db.multiDimensionalArrayProjection.find().pretty();This will produce the following output −{ "_id" : ObjectId("5cc6b75a9cb58ca2b005e66c"), "StudentFirstName" : "Chris", "StudentMarks" ... Read More
![Nishtha Thakur](https://www.tutorialspoint.com/assets/profiles/13598/profile/60_104893-1512719058.jpg)
92 Views
You can use aggregate framework. Let us first create a collection with documents −> db.topCountArrayDemo.insertOne( ... {"StudentId":101 , "StudentSubject": ["C", "MongoDB"]} ... ); { "acknowledged" : true, "insertedId" : ObjectId("5cc6b3209cb58ca2b005e669") } > db.topCountArrayDemo.insertOne( ... {"StudentId":102 , "StudentSubject": ["C", "Java"]} ... ); { "acknowledged" : true, "insertedId" : ObjectId("5cc6b3219cb58ca2b005e66a") } > db.topCountArrayDemo.insertOne( ... {"StudentId":103 , "StudentSubject": ["C", "MongoDB"]} ... ); { "acknowledged" : true, "insertedId" : ObjectId("5cc6b3229cb58ca2b005e66b") }Following is the query to display all documents from a collection with the help of find() method −> db.topCountArrayDemo.find().pretty();This will produce the following output −{ ... Read More
![Smita Kapse](https://www.tutorialspoint.com/assets/profiles/13597/profile/60_103706-1512718957.jpg)
131 Views
To create a user in MongoDB v3, use the createUser() method. This allows you to create a user and while creating you need to add user, password, and roles as well. These roles assign permissions. The syntax is as follows −use admin db.createUser( { user: “yourUserName", pwd: "yourPassword", roles: [ { role: "yourPermission", db: "yourDatabase" } ] } );Let us implement the above syntax in order to create a user In MongoDB v3 −> use admin switched to db admin > db.createUser( ... { ... ... Read More
![Anvi Jain](https://www.tutorialspoint.com/assets/profiles/13591/profile/60_98631-1512716973.jpg)
361 Views
To select two fields and return a sorted array with distinct values, use aggregate framework along with $setUnion operator. Let us first create a collection with documents −> db.sortedArrayWithDistinctDemo.insertOne( ... { value1: 4, value2: 5} ... ); { "acknowledged" : true, "insertedId" : ObjectId("5cc690b99cb58ca2b005e666") } > db.sortedArrayWithDistinctDemo.insertOne( ... {value1: 5, value2: 6} ... ); { "acknowledged" : true, "insertedId" : ObjectId("5cc690b99cb58ca2b005e667") } > db.sortedArrayWithDistinctDemo.insertOne( ... {value1: 7, value2: 4} ... ); { "acknowledged" : true, "insertedId" : ObjectId("5cc690b99cb58ca2b005e668") }Following is the query to display all documents from a collection with the ... Read More
![Nishtha Thakur](https://www.tutorialspoint.com/assets/profiles/13598/profile/60_104893-1512719058.jpg)
282 Views
You can use $type operator to check whether a filed contains null value. Let us first create a collection with documents. We have also inserted a null in a field −> db.nullDemo.insertOne({"FirstName":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5cc68a1eac184d684e3fa270") } > db.nullDemo.insertOne({"FirstName":null}); { "acknowledged" : true, "insertedId" : ObjectId("5cc68a25ac184d684e3fa271") } > db.nullDemo.insertOne({"FirstName":"Robert"}); { "acknowledged" : true, "insertedId" : ObjectId("5cc68a2cac184d684e3fa272") }Following is the query to display all documents from a collection with the help of find() method −> db.nullDemo.find().pretty();This will produce the following output. One of the field is null −{ "_id" : ObjectId("5cc68a1eac184d684e3fa270"), "FirstName" ... Read More
![Smita Kapse](https://www.tutorialspoint.com/assets/profiles/13597/profile/60_103706-1512718957.jpg)
468 Views
Let us first create a collection with a document −>db.useResultDemo.insertOne({"StudentFirstName":"Robert"}); { "acknowledged" : true, "insertedId" : ObjectId("5cda70f5b50a6c6dd317adcd") }Display all documents from a collection with the help of find() method −> db.useResultDemo.find();Following is the output −{ "_id" : ObjectId("5cda70f5b50a6c6dd317adcd"), "StudentFirstName" : "Robert" }Here is the query to use result from MongoDB in shell script with var keyword −> var studentName=db.useResultDemo.findOne({},{_id:0}); > studentNameFollowing is the output −{ "StudentFirstName" : "Robert" }
![Nishtha Thakur](https://www.tutorialspoint.com/assets/profiles/13598/profile/60_104893-1512719058.jpg)
67 Views
You can use INFORMATION_SCHEMA.COLUMNS for this. Let us first create a table −mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, Name varchar(20) ); Query OK, 0 rows affected (0.73 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(Name) values('Chris'); Query OK, 1 row affected (0.25 sec) mysql> insert into DemoTable(Name) values('Robert'); Query OK, 1 row affected (0.26 sec) mysql> insert into DemoTable(Name) values('Sam'); Query OK, 1 row affected (0.12 sec)Display all records from the table using select statement −mysql> select *from DemoTable;This will produce the following ... Read More
![Smita Kapse](https://www.tutorialspoint.com/assets/profiles/13597/profile/60_103706-1512718957.jpg)
563 Views
Use YEAR() and MONTH() to display records from specific month and year respectively. Let us first create a table −mysql> create table DemoTable ( CustomerId int NOT NULL AUTO_INCREMENT PRIMARY KEY, CustomerName varchar(20), CustomerTotalBill int, PurchasingDate date ); Query OK, 0 rows affected (0.83 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(CustomerName, CustomerTotalBill, PurchasingDate) values('John', 2000, '2019-01-21'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable(CustomerName, CustomerTotalBill, PurchasingDate) values('Chris', 1000, '2019-01-31'); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable(CustomerName, CustomerTotalBill, PurchasingDate) values('Robert', ... Read More