The equivalent syntax is as follows.db.yourCollectionName.find({}, {_id: 1, "column1": 1, "column2": 1}).pretty();To understand the above syntax, let us create a collection with the document. The query to create a collection with a document is as follows −> db.equivalentForSelectColumn1Column2Demo.insertOne({"CustomerName":"John", "CustomerAge":26, "CustomerCountryName":"US"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c92c6205259fcd19549980a") } ... Read More

To add elements to the AbstractCollection class, use the add() method. For example −absCollection.add("These"); absCollection.add("are"); absCollection.add("demo");To work with AbstractCollection class in Java, import the following package −import java.util.AbstractCollection;The following is an example to add elements to AbstractCollection class in Java −Example Live Demoimport java.util.ArrayList; import java.util.AbstractCollection; public class Demo { ... Read More

To list all collections in Mongo shell, you can use the function getCollectionNames().The syntax is as follows −db.getCollectionNames();You can use another command which is collections. The syntax is as follows −show collections;To list all collections in Mongo, use the above two functions. The query is as follows −> db.getCollectionNames();The following ... Read More

The containsAll() method checks for all the elements in the specified collection. It returns TRUE if this collection has all the elements. The methods check for each element one by one to see if it's contained in this collection.The syntax is as follows −public boolean containsAll(Collection c)To work with AbstractCollection ... Read More

To return query based on the date in MongoDB, let us take an example.To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −> db.returnQueryFromDate.insertOne({"PassengerName":"John", "PassengerAge":23, "PassengerArrivalTime":new ISODate("2018-03-10 14:45:56")}); {    "acknowledged" : true,    "insertedId" ... Read More

STL Priority Queue is the implementation of maxheap.This is a C++ program of STL priority queue for structure.AlgorithmBegin    Define a structure of type student.    Initialize variables in student structure.    Define another structure of type comparemarks    Overload the variables of student structure in comapremarks    structure.   ... Read More

The findAny() method of the IntStream class in Java is used to return an OptionalInt describing some element of the stream, or an empty OptionalInt if the stream is empty.The syntax is as follows −OptionalInt findAny()Here, OptionalInt is a container object which may or may not contain an int value.Create ... Read More

You can use updateMany() to update documents. Let us create a collection with a document. The query to create a collection with a document is as follows −> db.updateManyDocumentsDemo.insertOne({"StudentName":"John", "StudentLastName":"Smith"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c948edd4cf1f7a64fa4df48") } > db.updateManyDocumentsDemo.insertOne({"StudentName":"John", "StudentLastName":"Doe"}); {    "acknowledged" : true,    "insertedId" ... Read More

The unordered_multimap reserve() function in C++ STL sets the number of buckets in the container to the most appropriate number so that it contains at least n elements.If n is greater than the current numbers of bucket multiplied by the max_load_factor, the container’s number of buckets is increased and a ... Read More

unordered_multimap swap() function in C++ STL is used to swap the elements of one multimap to another of same size and type.AlgorithmBegin    Declaring two empty map container m, m1.    Insert some values in both m, m1 map containers.    Perform swap() function to swap the values of m, ... Read More