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

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

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

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

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

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

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

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" }

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

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