ETL Interview Questions and Answers, ETL Interview Questions and Answers Freshers, ETL Interview Questions and Answers, ETL Interview Questions

Before getting on to the ETL interview questions, the student must know that the ETL is a continuously varying field which needs the students as well as professionals to upgrade their skills with the new features and knowledge, to get fit for the jobs associated with ETL. This post related to ETL Interview Questions and Answers, ETL Interview Questions and Answers Freshers, ETL Interview Questions and Answers, ETL Interview Questions will help you let out find all the solutions that are frequently asked in you upcoming ETL interview.

Over thousands of vacancies available for the ETL developers, experts must be acquaintance with all the component of ETL technologies. This is necessary for the students in order to have in-depth knowledge of the subject so that they can have best employment opportunities in the future. Knowing every little detail about ETL is the best approach to solve the problems linked with problem.

APTRON has spent hours and hours in researching about the ETL Interview Questions and Answers, ETL Interview Questions and Answers Freshers, ETL Interview Questions and Answers, ETL Interview Questions that you might encounter in your upcoming interview.  All these questions will alone help you to crack the interview and make you the best among all your competitors.

First of all, let us tell you about how the ETL technology is evolving in today’s world and how demanding it is in the upcoming years. In fact, according to one study, most of the companies and businesses have moved to the ETL. Now, you cannot predict how huge the future is going to be for the people experienced in the related technologies.

Hence, if you are looking for boosting up your profile and securing your future, ETL will help you in reaching the zenith of your career. Apart from this, you would also have a lot of opportunities as a fresher.

These questions alone are omnipotent. Read and re-read the questions and their solutions to get accustomed to what you will be asked in the interview. These ETL interview questions and answers will also help you on your way to mastering the skills and will take you to the giant world where worldwide and local businesses, huge or medium, are picking up the best and quality ETL professionals.

This ultimate list of best ETL interview questions will ride you through the quick knowledge of the subject and topics like ETL-Extract, Transform, Load, ETL TOOLS. This ETL interview questions and answers can be your next gateway to your next job as a ETL expert.

These are very Basic ETL Interview Questions and Answers for freshers and experienced both.

Q1: What is ETL?
A1: In data warehousing architecture, ETL is an important component, which manages the data for any business process. ETL stands for Extract, Transform and Load. Extract does the process of reading data from a database. Transform does the converting of data into a format that could be appropriate for reporting and analysis. While, load does the process of writing the data into the target database.

Q2: Explain what are the ETL testing operations includes?
A2: ETL testing includes

  • Verify whether the data is transforming correctly according to business requirements
  • Verify that the projected data is loaded into the data warehouse without any truncation and data loss
  • Make sure that ETL application reports invalid data and replaces with default values
  • Make sure that data loads at expected time frame to improve scalability and performance

Q3: Mention what are the types of data warehouse applications and what is the difference between data mining and data warehousing?
A3: The types of data warehouse applications are

  • Info Processing
  • Analytical Processing
  • Data Mining

Data mining can be define as the process of extracting hidden predictive information from large databases and interpret the data while data warehousing may make use of a data mine for analytical processing of the data in a faster way. Data warehousing is the process of aggregating data from multiple sources into one common repository

Q4: What are the various tools used in ETL?

  • Cognos Decision Stream
  • Oracle Warehouse Builder
  • Business Objects XI
  • SAS business warehouse
  • SAS Enterprise ETL server

Q5: What is fact? What are the types of facts?
A5: It is a central component of a multi-dimensional model which contains the measures to be analysed. Facts are related to dimensions.

Types of facts are

  • Additive Facts
  • Semi-additive Facts
  • Non-additive Facts

Q6: Explain what are Cubes and OLAP Cubes?
A6: Cubes are data processing units comprised of fact tables and dimensions from the data warehouse. It provides multi-dimensional analysis.

OLAP stands for Online Analytics Processing, and OLAP cube stores large data in muti-dimensional form for reporting purposes. It consists of facts called as measures categorized by dimensions.

Q7: Explain what is tracing level and what are the types?
A7: Tracing level is the amount of data stored in the log files. Tracing level can be classified in two Normal and Verbose. Normal level explains the tracing level in a detailed manner while verbose explains the tracing levels at each and every row.

Q8: Explain what is Grain of Fact?
A8: Grain fact can be defined as the level at which the fact information is stored. It is also known as Fact Granularity

Q9: Compare ETL & ELT

Criteria ETL ELT
Flexibility High Low
Working methodology Data from source system to data warehouse Leverages target system to transform data
Performance Average Good

Q10: How many steps are there in ETL process?
A10: In ETL process data is extracted from source such as the database servers and it is used to generate business roll.

Q11: What are the steps involved in ETL process?
A11: The steps involved are defining the source; target, creating the mapping, creating the session, and creating the workflow.

Q12: Can there be sub steps of ETL steps?
A12: Each of the steps involved in ETL has several sub steps. The transform step has most sub steps.

Q13: What is initial load and what is full load?
A13: In ETL the initial load is the process for populating all data warehousing tables for very first time. Full load means when the data is loaded for the first time all set records are loaded at a stretch depending on its volume. It would erase all contents in the table and would reload fresh data.

Q14: What is meant by incremental load?
A14: Incremental load refers to applying the dynamic changes as and when required in a specific period and predefined schedules.

Q15: What are three tier systems in ETL?
A15: The data warehouse is considered to be the three tier system in ETL.

Q16: What are the three tiers in ETL?
A16: Middle layer in ETL provides the data that is usable in a secure way to end users. Other two layers are on the other side of the middle tier, the end user and back end data storage.

Q17: What are the names of the layers in ETL?
A17: The first layer in ETL is the source layer and it is the layer where data lands. Second layer is integration layer where data is stored after transformation. Third layer is the dimension layer where actual presentation layer stands.

Q18: What are Dimensions?
A18: Dimensions are the groups or categories through which the summarized data are sorted.

Q19: What is Staging area referring to?
A19: Staging area is the place where the data is stored temporarily in the process of Data Integration. Here, the data s cleansed and checked for any duplication.

Q20: Explain ETL Mapping Sheets.
A20: ETL mapping sheets contains all the required information from the source file including all the rows and columns. This sheet helps the experts in writing the SQL queries for the ETL tools testing.

Q21: Mention few Test cases and explain them.

  • Mapping Doc Validation – Verifying if the ETL information is provided in the Mapping Doc.
  • Data Check – Every aspect regarding the Data such as Data check, Number Check, Null check are tested in this case
  • Correctness Issues – Misspelled Data, Inaccurate data and null data are tested.

Q22: List few ETL bugs.
A22: Calculation Bug, User Interface Bug, Source Bugs, Load condition bug, ECP related bug.

In addition to the above ETL testing questions, there may be other vital questions where you may be asked to mention the ETL tools which you have used earlier. Also, you might be asked about any debugging issues you have faced in your earlier experience or about any real time experience.

Q23: How ETL Testing is different from database testing?
A23: The following table captures the key features of Database and ETL testing and their comparison −

Function Database Testing ETL Testing
Primary Goal Data validation and Integration Data Extraction, Transform and Loading for BI Reporting
Applicable System Transactional system where business flow occurs System containing historical data and not in business flow environment
Common Tools in market QTP, Selenium, etc. QuerySurge, Informatica, etc.
Business Need It is used to integrate data from multiple applications, Severe impact. It is used for Analytical Reporting, information and forecasting.
Modeling ER method Multidimensional
Database Type It is normally used in OLTP systems It is applied to OLAP systems
Data Type Normalized data with more joins De-normalized data with less joins, more indexes and Aggregations.

Q24: What are the different ETL Testing categories as per their function?
A24: ETL testing can be divided into the following categories based on their function −

  • Source to Target Count Testing − It involves matching of count of records in source and target system.
  • Source to Target Data Testing − It involves data validation between source and target system. It also involves data integration and threshold value check and Duplicate data check in target system.
  • Data Mapping or Transformation Testing − It confirms the mapping of objects in source and target system. It also involves checking functionality of data in target system.
  • End-User Testing − It involves generating reports for end users to verify if data in reports are as per expectation. It involves finding deviation in reports and cross check the data in target system for report validation.
  • Retesting − It involves fixing the bugs and defects in data in target system and running the reports again for data validation.
  • System Integration Testing − It involves testing all the individual systems, and later combine the result to find if there is any deviation.

Q25: Explain the key challenges that you face while performing ETL Testing.

  • Data loss during the ETL process.
  • Incorrect, incomplete or duplicate data.
  • DW system contains historical data so data volume is too large and really complex to perform ETL testing in target system.
  • ETL testers are normally not provided with access to see job schedules in ETL tool. They hardly have access on BI Reporting tools to see final layout of reports and data inside the reports.
  • Tough to generate and build test cases as data volume is too high and complex.
  • ETL testers normally doesn’t have an idea of end user report requirements and business flow of the information.
  • ETL testing involves various complex SQL concepts for data validation in target system.
  • Sometimes testers are not provided with source to target mapping information.
  • Unstable testing environment results delay in development and testing the process.

Q26: What are your responsibilities as an ETL Tester?
A26: The key responsibilities of an ETL tester include −

  • Verifying the tables in the source system − Count check, Data type check, keys are not missing, duplicate data.
  • Applying the transformation logic before loading the data: Data threshold validation, surrogate ky check, etc.
  • Data Loading from the Staging area to the target system: Aggregate values and calculated measures, key fields are not missing, Count Check in target table, BI report validation, etc.
  • Testing of ETL tool and its components, Test cases − Create, design and execute test plans, test cases, Test ETL tool and its function, Test DW system, etc.

Q27: What do you understand by the term ‘transformation’?
A27: A transformation is a set of rules which generates, modifies, or passes data. Transformation can be of two types − Active and Passive.

Q28: What do you understand by Active and Passive Transformations?
A28: In an active transformation, the number of rows that is created as output can be changed once a transformation has occurred. This does not happen during a passive transformation. The information passes through the same number given to it as input.

Q29: What is Partitioning? Explain different types of partitioning.
A29: Partitioning is when you divide the area of data store in parts. It is normally done to improve the performance of transactions.
If your DW system is huge in size, it will take time to locate the data. Partitioning of storage space allows you to find and analyze the data easier and faster.
Parting can be of two types − round-robin partitioning and Hash partitioning.

Q30: What is the difference between round-robin partitioning and Hash partitioning?
A30: In round-robin partitioning, data is evenly distributed among all the partitions so the number of rows in each partition is relatively same. Hash partitioning is when the server uses a hash function in order to create partition keys to group the data.

ETL Conclusion Interview FAQs

We know the list of ETL Interview Questions and Answers, ETL Interview Questions and Answers Freshers, ETL Interview Questions and Answers, ETL Interview Questions is overwhelming but the advantages of reading all the questions will maximize your potential and help you crack the interview. The surprising fact is that this ETL interview questions and answers post covers all the basic of the ETL technology and you have to check out the FAQs of different components of ETL too.

However, you will be asked with the questions in the interview related to the above mentioned questions. Preparing and understanding all the concept of ETL technology will help you strengthen the other little information around the topic.

After preparing these interview questions, we recommend you to go for a mock interview before facing the real one. You can take the help of your friend or a ETL expert to find the loop holes in your skills and knowledge. Moreover, this will also allow you in practicing and improving the communication skill which plays a vital role in getting placed and grabbing high salaries.

Remember, in the interview, the company or the business or you can say the examiner often checks your basic knowledge of the subject. If your basics is covered and strengthened, you can have the job of your dream. The industry experts understand that if the foundation of the student is already made up, it is easy for the company to educate the employ towards advance skills. If there are no basics, there is no meaning of having learnt the subject.

Therefore, it’s never too late to edge all the basics of any technology. If you think that you’ve not acquired the enough skills, you can join our upcoming batch of ETL Training in Noida. We are one of the best institute for ETL in noida which provide advance learning in the field of ETL Course. We’ve highly qualified professionals working with us and promise top quality education to the students.

We hope that you enjoyed reading ETL Interview Questions and Answers, ETL Interview Questions and Answers Freshers, ETL Interview Questions and Answers, ETL Interview Questions and all the FAQs associated with the interview. Do not forget to revise all the ETL interview questions and answers before going for the ETL interview. In addition to this, if you’ve any doubt or query associated with ETL, you can contact us anytime. We will be happy to help you out at our earliest convenience. At last, we wish you all the best for your upcoming interview on ETL Technology.