infosys
What are joins in SQL?
A JOIN clause is used to combine rows from two or more tables, based on a related column between them. It is used to merge two tables or retrieve data from there. There are 4 joins in SQL namely: Inner Join - It is used to return all the rows from multiple tables where the join condition is satisfied. Right Join is used to return all the rows from the right table but only the matching rows from the left table where the join condition is fulfilled. Left Join is used to return all the rows from the left table but only the matching rows from the right table where the join condition is fulfilled. Full Join returns all the records when there is a match in any of the tables. Therefore, it returns all the rows from the left-hand side table and all the rows from the right-hand side table. cross join is a product gives result set of
What is a Primary key?
A Primary key Uniquely identifies a single row in the table - Null values not allowed while a unique key can be made up of several columns and null values are allowed
What are classes?
Class are templates for creating objects, objects represent real life entities, they have a state(what it knows;age color) and behavior(what it does; bark chew) - only 1 Class but can have many objects; When an object of a class is created, the class is said to be instantiated.
What is composition?
Composition is design modelling to built a HAS relationship, example, a computer has a ram but a ram is not a computer, a vehicle has doors but doors are not vehicles. -This also provides us with option to re use code, ram is reusing the ram object or door object
Data Access Object Pattern
DAO pattern is used to separate low level data accessing API or operations from high level business services.
What are the different subsets of SQL? DDL DML DCL
DDL (Data Definition Language): It allows you to perform various operations on the database such as CREATE, ALTER and DELETE objects. DML ( Data Manipulation Language) - It allows you to access and manipulate data. It helps you to insert, update, delete and retrieve data from the database. DCL ( Data Control Language) - It allows you to control access to the database. Example - Grant, Revoke access permissions.
What is a data warehouse?
Data warehouse is the storage of organization's historical data so it can be analyzed
What is the difference between DELETE and TRUNCATE statements?
Delete Is used to delete row in table, it can rollback data after using delete statement, it is a DML command Truncate is used to delete all the rows of table, it cannot rollback data and is a DDL command, it is faster.
Durability.
Durability means that once a transaction has been committed, it will remain so
What are HDFS?
HDFS is the storage unit in hadoop, stores data in different blocks in a distributed environment, Namenode is the masternode and stores metadata information, like block location and repitation factors Datanode is slave nodes which are responsible for storing data
Analyzed High Level Design (HLD), Low Level Design (LLD)
HLD is an overall system design, to see functional design and LLD This is a detailed phase, the project is broken into modules and programs;
Requirement Analysis
Here you will work closely with the customer; focus on what and not on how; identify the problem to be solved. Break down environment as functional and non functional; . This should answer following questions? -What function does software do? -What should be the expected behavior of the software? -What are the interfaces and performance expectations?
What is a foriegn key?
It is a reference to a parent and child relationship between tables- used as a constraint
What is the difference between JDK and JVM?
Java Development Kit (JDK) is for development purpose and JVM is a part of it to execute the java programs. JDK provides all the tools, executables and binaries required to compile, debug and execute a Java Program. The execution part is handled by JVM to provide machine independence.
What is the difference between JVM and JRE?
Java Runtime Environment (JRE) is the implementation of JVM. JRE is the container of JVM
What is JVM and is it platform independent?
Java Virtual Machine (JVM) is the heart of java programming language. JVM is responsible for converting byte code into machine readable code.
Tell me about the various Hadoop daemons and their roles in a Hadoop cluster.
Namenode is the masternode stores the metadata of files and directories, knows blocks that make a file and where the blocks are located in cluster Datanode is the slave node which contains the actual data Secondary Namenode is a backup of the datanode it periodically merges changes present in namenode, used in case namenode fails. ResourceManager managers resources and schedule applications running on top of YARN Nodemanager runs on slave machines is responsible for execution of tasks on each datanode, and monitoring their resource usages JobHistoryServer maintains information about mapReduce jobs after it termintes.
what is Normalization and what are the advantages of it?
Normalization is the process of organizing data to avoid duplication and redundancy. Some of the advantages are: Better Database organization More Tables with smaller rows Efficient data access
What does OLAP stand for?
OLAP stands for On Line Analytical Processing. It which collects, manages, and processes for anaylsis
What does OLTP stand for?
OLTP stands for On Line Transaction Processing. It is a system which modifies the data whenever it received. concurrently running of multiple sections.
Java Virtual Machine (JVM), Java Runtime Environment (JRE), Java Development Kit (JDK)
The JRE is a java runtime environment, it provides the minimum requirements for executing a java application. - The JVM is a Java virtual ma
How would you retrieve a count of all items in an SQL table?
The SQL COUNT() function is particularly useful because it allows you to count database records based on user-specified criteria. You can use it to count all the records in a table, count unique values in a column, or count the number of times records occur that meet certain criteria.
Consistency.
The consistency brings state from one valid to another
Isolation.
The isolation property ensures that the concurrent execution of transactions results in a system state so a transcation is done one after another another
Testing phase
The testing phase involves static testing and dynamic testing. Static testing; Is done without executing, examines and conducts inspection of testing documents. Dynamic Testing; Executes and compares, expected results with the actual results.
development Phase
This is where you are building actual source code; have database integration; interface representation
What type of loops exist in java?
While loop is runs until the boolean condition is met while(boolean condition) { loop } -for loop provide a clear way to write a loop you have a initialize condition, a termination condition and a increment/decrement and your statement will run until the termination condition is met do while: do while loop is similar to while loop with only difference that it checks for condition after executing the statements- do while starts by executing statements and then checking condition
What are YARN?
Yet another resource negotiator, is a framework which manages resources and provides execution environment for processes. Resourcemanager- it allocates resources based on needs as receives the processing request and passes the part of requests to nodemanagers where the processing takes place. Nodemanager is responsible for execution task on each datanode
3 Qualities of a Strong Leader
communcation emathaze assertiveness
What is inheritance?
if we have 2 basic classes such as car and vehicle, they have an IS relationship, car is a vehicle, Car extends from vehicle. -the car class can use all the fields and methods of a vehicle class, and now we can focus on making the car class code unique
Implementation phase
in this phase you have to get software accepted and install the software at the customer site.
abstract class vs interface
interface is only the set of behaviors; interfaces can be multi inherited but an abstract class is a set of behavior and states abstract classes can not be multi inherited
What is a star schema?
is used to simplify complix normalized set of tables into one database structure is where a single fact table references number of dimension tables, keys from all dimension tables flow into fact table facts are things events that occurs, brought sold etc dimensions are nouns and objects they can be thought of as things
What is a snow flake schema?
ust like the star schema, a single fact table references number of other dimension tables in snow flake scheme. Here however, these dimension tables are further normalized into multiple related tables. As these tables are further snow flaked into smaller tables, this schema is called a snow flake schema
List some of the functions performed by OLAP.
"roll-up", "drill-down", "slice", "dice", and "pivot".
What is Encapsulation?
-Lets your restrict access to certain components in the objects you're creating, stopping classes outside the class you're working on. Example if you have a player class where health is define, you don't want someone to redefine the total health in the main class. -You can do this by using private access modifiers and use getters to return values to main method
DBMS`
A DBMS allows a user to interact with the database. The data stored in the database can be modified, retrieved and deleted and can be of any type like strings, numbers, images etc. Relational Database Management System: The data is stored in relations (tables). Example - MySQL.
List and explain each of the ACID properties that collectively guarantee that database transactions are processed reliably.
ACID (Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably. They are defined as follows:
What is abstractions?
Abstraction is a process of hiding the implementation details and showing only functionality to the user. - example when you write an email you all the back end protocols are hidden you only see the functionality of writing the email
What is Polymorphism?
Allows actions to act differently Overriding is known as run time polymorphism
What is Apache Oozie?
Apache Oozie is a scheduler which schedules jobs Oozie Workflow: These are sequential set of actions to be executed. Like a relay race Oozie Coordinator: These are the Oozie jobs which are triggered when the data is made available to it.
What is Apache ZooKeeper?
Apache ZooKeeper coordinates with various services in a distributed environment. It saves a lot of time by performing synchronization, grouping and naming.
What is Hadoop and its components
Apache hadoop is the solution to the big data problem, it's a framework that lets us store and process big data, consists of HDFS(namenode, datanode) and YARN(Resourcemanger, nodemanger)
Atomicity.
Atomicity mean all or nothing, the transaction must complete or database state is left unchanged.
Explain "Big Data" and what are five V's of Big Data?
Big data is a collection of large and complex data sets which make it difficult to process in RDBMS, It is difficult to capture, store, analyze and visualize the big data. Volume, Velocity, Variety,Veracity,Value
how aggregation is different than composition
Both are speical type of association and differ in weight of realtionship Composition, is stronger form of "is part of" relationship compared to aggregation "has a" . In composition, the member object can not exist outside of the enclosing class while same is not true for Aggregation.
Give some examples for OOPS 4 pilars
Encapsulation, Abstraction, Polymorphic and Inheritance
What are the 4 principles of OOP,
Encapsulation- Is hiding of data implementation by restricting access to public methods Abstraction - a concept which is not associated with any particular instance. This express the intent of the class rather than the actual implementation, So one class should not know the inner details of another in order to use it, knowing interfaces is enough inheritance- expresses "is a" relationship between two objects, Polymorphism - means one name many forms, can be static or dynamic, static polymorphism is achieved using method overloading and dynamic polymorphism is using method overriding.
Describe different normalization form.
First Normal Form (1NF) - No repeating groups within rows Second Normal Form (2NF) - Every non-key (supporting) column value is dependent on the whole primary key. Third Normal Form (3NF) - Dependent solely on the primary key and no other non-key (supporting) column value.
Design
Focus on how, breaks into smaller parts, decide how each component works and how they will work together
Maintenance phase
Phase is for all modifications which do not meet customer requirement or to for adding new feature to current system. Also all corrections for the project or product take place in this phase.
Recursion
Recursion in java is a process in which a method calls itself continuously, public class RecursionExample3 { static int factorial(int n){ if (n == 1) return 1; else return(n * factorial(n-1)); } public static void main(String[] args) { System.out.println("Factorial of 5 is: "+factorial(5)); } }
List the types of OLAP servers.
Relational OLAP Multidimensional OLAP Hybrid OLAP Specialized SQL Servers
What are the steps in SDLC
SDLC produce a high-quality software that meets customer expectations, reaches completion within times and cost estimates. - Requirement Analysis -Design, -Development -Testing, - Implementation - Maintenance
Difference between String, StringBuffer and StringBuilder?
String is immutable and final in java, so whenever we do String manipulation, it creates a new String. String manipulations are resource consuming, so java provides two utility classes for String manipulations - StringBuffer and StringBuilder. StringBuffer and StringBuilder are mutable classes. StringBuffer operations are thread-safe and synchronized where StringBuilder operations are not thread-safe. So when multiple threads are working on same String, we should use StringBuffer but in single threaded environment we should use StringBuilder. StringBuilder performance is fast than StringBuffer because of no overhead of synchronization.
Explain types of SDLC.
Typically uses Waterfall or Agile methodology, in the waterfall model each phase must be completed before moving to the next phase can begin, and it's advantages are clear stages but disadvantage is adjustment can end the project, it is not flexible. -Agile Methods break the product into small incremental builds. These builds are provided in iterations. Each iteration typically lasts from about one to three weeks. -the advantages are Promotes teamwork and cross training and communication; Good model for environments that change steadily. the disadvantages are Depends heavily on customer interaction, so if customer is not clear, team can be driven in the wrong direction.
What does UNION do? What is the difference between UNION and UNION ALL?
UNION merges the contents of two structurally-compatible tables into a single combined table. The difference between UNION and UNION ALL is that UNION will omit duplicate records whereas UNION ALL will include duplicate records.
Explain 5 v's of big data?
Volume is the amount of growing data at exponential rate(peta/exabytes) Velocity is the rate at which data is being produced, social media the biggest reason for this, Variety is the different types of data types(Mp3, doc) Veracity is the uncertaincity of data available due to incompleteness or inconsistancy, because of volume there is too much to swift through Value is the turn big data into something of value, adding RIO for the company
What is the difference between the WHERE and HAVING clauses?
When GROUP BY is not used, the WHERE and HAVING clauses are essentially equivalent. However, when GROUP BY is used: The WHERE clause is used to filter records from a result. The filtering occurs before any groupings are made. The HAVING clause is used to filter values from a group
What is overloading and overriding in java?
When we have more than one method with same name in a single class but the arguments are different, then it is called as method overloading. - Overloading is known as compile time polymorphism Overriding concept comes in picture with inheritance when we have two methods with same signature, one in parent class and another in child class. We can use @Override annotation in the child class overridden method to make sure if parent class method is changed, so as child class. Overriding is known as run time polymorphism
What are active and passive "NameNodes"?
active namenode the working node and passive comes alive if active fails
whats an array?
an array stores a sequential collection of elements of same type and is used to store sequential data. Arrayed are usually a fixed sized, arraylist are dynamic in size and you can add to them.